depends. i have 2 lvl 160 + accounts. 1 has no princess yet and the other has a themis...which i don't even use at the moment. Princesses CAN be replaced by valks , barbarians and even magic fencers. Most of the times , u need a general duelist to block a strong boss because u will rarely have a princess just 1v1 it anyawy , and for that , there are enough units that can fill that niche. That being said , a magic fencer can act like a princess in melee for a short time because they change their attacks to magical (so they ignore armor just like a princess)...but all that requires you to make adjustments , which is not easy if your acount is low level. Having a princess makes it all easier