The thing is, if you play full offense, the opponent have to think about those things you said too.
So if an alliance of 50+ strong players who have the largest offensive capability on the server state in public that they will respond to any approaching, even scouting with full scale attack, targeting all resource and crop fields (no need to target buildings), the would be attacker will have to think about this. That is the form of defense the full offensive approach represents, a threat of stronger counter attack than your attack.
So, when planning to even scout an alliance like that, you have to think about the consequenses. As in, do you want to lose up to 80% of the resource production you or your alliance have and most likely around 1/3 of your troops + face starvation.
If you are in position to do so, you can even state that the retaliation will be used against everyone in the alliance of the player who scout, raid or attack any of the alliances villages or those under its "protection". This way the opposing Kings might be very clear to their vassals, to never scout that alliance. So when you even scout to notice that they have "no defenses", you will be struck bad as a response.
If you would be amassing defensive troops, you would not have that capablity. You only have it because others make part defense part attack, and you go full offense as an alliance. You of course should secure the best farms to raid more, and grow more. You have better capabilities for that if you play strong offense vs defensive or balanced play.
So you use the threat of your counter invasion as a defense.
This is probably a strategy no one uses, or have used before to that extent. So you really do not know how that would go.
To some extent, every large alliance uses a threat of their counter attack as a defense. Even the balanced or defensive types. The weight of the threat however is different if you use your resources on offense.
The ability to Fake Attacks makes this even stronger. Even the opponent uses heavy Scouting and you wont, they wont know what or how its going to happen and you are the one who knows it instead. You can also either hit the capitals with strong forces or leave them all under fake attacks, as the defenses will probably pile up on these cities. This way the smaller armies that you have plenty, that are made instead of defensive armies, will cause havoc on smaller settlements, and sometimes utterly destroy them. Or target one capital with strong force, and leave others under Fake Attacks to give a message, that capitals are not safe, and to force the defensive troops to pile on these locations. Lets say an alliance that had around 500 villages and is hit so that either 450 of them lose all production, or are destroyed, leaving 50 player alliance with 49 cities (50 capitals minus one). They cannot win anymore. Might be you cannot either, but you probably still fare better than them. So the question is, do you really want to Scout ?
If your alliance is not one of the biggest in the server, you cannot hold this policy. Its way harder to do this alone, but a large group of strong people can easily do this, or a similar thing.
And of course, if someone wants to join playing defensively in such an alliance, accepting it would help to grow the alliance in power, but to convince that person to produce attacking and raiding armies instead would benefit it more. A Scouting player would probably be more benefical than a defensive one, but if you think about it, those scouting armies could also be attack armies too which means, more potential for destroyed resource fields or crops for the opponent. It really does not matter where the opponent have its defenses that much, as you hit all but capitals and the scouting and moving the defensive armies is another mind game you do not have to be part of if you do not want to. The defensive troops you scout might as well not be there when your armies arrive, so better that there are more armies that do than not. Alliances probably invest heavily on protecting their villages from Scouting, especially the ones that matter so, you can just let them and have more attacking troops instead for their to worry about. You can still use scouts as minor squads for raiding and general information.
Lets say you have 10 cities and made 9 offensive armies in each of them. One larger from capital that you support with 1 city, and 8 smaller ones. Lets say all of your 50 allies have similar composition and same amount of vllages than the opposing alliance. That amouts to 50 larger armies and 400 smaller ones. The opposing alliance probably have as little as 100 larger armeis and 50 smaller ones at most. Rest of them are Scouts and Defensive troops, or so called support cities with no army at all. It wont matter if you lose one or two armies, you just build them again and still have more than the opponent. They will defend their capitals and their capitals contain their so called "Hammer" which cannot be in the city as your attacks start arriving, so draining the defensive troops from other cities to capital.
You dont need to raid with raid specific troops or so called Raiding Armies. You have so many offensive ones that you can just use them, it makes no difference. The thing that matters, is that when your alliance goes full offense, all your troops are the best attack types of your given Tribe. Raid units and defensive units go obsolate fast, and scouts are probably as far as i understand, always obsolate beyond raiding. The only units that should matter in the end, are the amount of best fully upgraded attacking units and siege engines you have. The thing might be different in Legends, as you need to protect the Wonder as a team. Alternatively, you could always aim to destroy otrhers and never make one yoruself, but then you cannot win in there as the winning condition is upgrading that building to 100. In Kingdoms i believe, you gain the winning condition by acquiring resouroces through offense.
Because of this, i would not choose Gaul as a Tribe in that kind of Alliance, only Romans and Teutons. Still, the Gauls seem to be the most popular Tribe. If you really want 1/9 of your armies to be defensive, Teutons have the best anti cavalry and Romans have the best anti infantry. These could be piled up where the Treasures are located to gain as many armies as there would be members. So each would have one defensve army full of either Spearmen or Pretorian.
If you want to have different offensive roles, then one or more persons might build one larger army and fewer smaller ones, and the rest would build the armies that raid and attack in bulk.
PS. Another Idea: If 2 server would start at the exact same time, the End Game could be the two servers battling it out, and only the winning server would "win" and the winning players would be the top of the winning server.
PS 2. I do not have to research a game involving military strategy much, as i have a lot of experience in this. The game i usually play is Steel Panthers. So building armies and using your "points" efficiently is known to me. It is a game where you choose an army with same point value than your opponent, trying to evaluate what your opponent will do, and then deploy that army and do a battle as turn based military simulation. One thing i have learned, that min maxing your resources and just guessing with pure instinct and experience is way more efficient with a given point limit than actually investing on information gain or similar means - Just use the points to gain more regular troops instead, you will need them. Also, having more brute force almost always wins, especially if you know how to use it. There are also many mind games you can just ignore. But in Steel Panthers, the advantage is strongly in defensive positions, so the best attack is to advance fast and establish the defensive position as far as possible in the same time than flanking and controlling your opponents movement with artillery. To have more assets for this is in my opinion almost always better than specialized and expensive approach with less units. This is the mind set i think also Travian with, but in Travian the stance is different: Defend with Offense when in Steel Panters it is to make offense with defense. In setting like Travian that would probably mean you encircle a city and make a blockade to starve it out, but the game mechanics wont allow that. Then you would of course do it with using defensive troops, and when the opponent tries to break that containment they would have to attack on your position. This would change the way you would have to think about defensive units when the mind is set on offense.
In terms of Travian, the "Points" you have in use means Crop - As in how many troops your crops can support, and this is your supply. To use your supply as efficient as possible is a choise you have to make. It makes up your Troop Composition, which you want to be more efficient than the opponent. If you gain an advantage, multiply it 50 times in an alliance and the advantage grows even wider.
RTS Type of games have this same approach. They have Supply Limits and sometimes the players even destroy their own troops on purpose to free up supply for a better composition.