"Going back to the question, a deck without many different strategy combinations will suffer that fate pretty quickly. And it's hard to think of ideas to give a deck some "personality" (the "strong" deck, the "summon" deck, the "support" deck, the "magic" deck) without making it feel like you are going for the same strategy every time."
If you want to avoid that fate combination, you can aways add some neltral units, that appear in any deck, also allow, or even make mandatory to combine classes to make your deck.
You could even add a mode that you make your full deck based on in game decisions like this:
tier 1 all neltral/inicial-class, after you get to tier 2 you choose from 2 or 3 differents classes which one do you like to add to your deck, same happens for tier 3 and foward. So you can play with a assassing priest or a mage hunter.
also, you can make some monsters imune to somethings in order to discorage purely focused strategies.