I do agree that it is slightly weaker on speed since there is more troops involved even in mass plundering.
However since crop production is higher you can increase the reinforcement amount to about 3-4x more units than above and you get about the same results.
OFC the losses would be shared across a lot of players so you would not loose everything, but the losses would be sufficiently big that there would be no economic gain from doing it.
I doubt the trades would be favourable for the attacker.
First of all farms are generally very small pop, this means on average they will recieve quite a decent morale bonus up to 50% (at about 8 times more pop on attacker).
Second even though we wont have a lot of wall for most of the attacks the defending force will have a clear troop superiority which will result in really really favourable trades for the defenders since there is no hero or no weapon involved.
This is a pretty realistic scenario of how most of the defences would look like
And as you can see the losses of the attacker is more than twice of the defender. And phalanx+druid composition is pretty close to a balanced deff force so it works just as well against clubs