I just go to the forums, look at the most popular unit for a certain level, and... I see the same thing over and over. Seriously, who would fight with an army that only has one level 4 (or 5, it doesn't matter) unit? Players have armies! Many different types of troops, and each type plays its own role!!! And how useful it is depends on the player's skill! Personally, I don't even use just one type of troop at the beginning. As for cavalry, they are very useful, especially the ones riding on lizards.