As wiki is introducing about this game, good in defense are Gauls. And Gauls are recommended for those with less time.
Romans are in the middle on the road between defense and offense. Their troops are more expensive (that's why I recommend starting with infantry), however also a good start.
Teutons are most used in offense by "non-stop" players while they don't have a well defense buildings like Gauls do. And no one mentioned a guide on how to use Teutons as defense player. Their advantage is that they can build more troops. However, it is easier to destroy the defense of a Teuton who don't know to play (yep, good idea).
In my guide I wanted to attract attention to some details which are not used generally by beginners.
"In theory, that should work". Maybe. Use simulator too, practice, calculate and compare the effects.
Yes, you can train Druidriders in same time as training Phalanxes for a faster time. I didn't said that you don't have to use cavalry.
However, a full "hammer attack" could kill a large amount of troops.
Using simulator, I concluded how it could be more efficient to use troops in defense and to kill a lot more of the attacking army while defending. While you're at home, not far away in distance.