And If you really want to make pure thematic decks, It can also be very tricky, I mean, take the warior hero by exemple:
the player knows thet he needs to make units fhysically stroger, but how you gonna do this can variate a lot:
you can focus on base heath, or healing, or armor, or on damage and health, or suport, or progressive in-battle growth, or defending the glass cannon with a defensive unit, or groing units mostly with wepons/itens, or with special units that get stronger with numbers. So are you going to bet on many week units because of that special unit? do you prefer bet on the glass cannon + the defender? do you have enough tanks to afford a in-game growth unit? damage with the HP pays the risk? what if there are lots of ranged monsters? are you strong enough to get there with a lot HP?Is It better to use your sacrifice spell to do a big damage with the higth Hp unit or It would be more useful alive?