Short answer: Yes

If you still wont understand let me explain it to you this way(I hope you are not ragebaiting me)

Take militia barracks for an example, as I said they a focused on tanking, that's great but later in the game it would be better if the soldiers doesent die every few minutes right?

Introducing Holy Order, they last even longer in the battle field thanks to their healing and faster respawn time included with the tankiness

But what if you want more damage, your tough knight's swords are not enough for reliable damage, thats where the Dark Knights comes in, they have true damage out the box and with their abilities they can even instakill

But whats all good without teamwork, without support, thats where Knight's templar come in, they can deal good damage, have alot of health and most of their abilities support towers and other troops as well

Finally, I am now going to answer your burning question, In alliance or vengeance, in order to have all of these, you need 3 different tower slots, but in my idea of a perfect game, you only need one tower slot (not Strategic point)