If for example you would play without Simon's avatar or character cards, you wouldn't be able to heal at all.
But doesn't that mean you never want to play with Simon as a main for the same reason, you need his cards?
It seems strange to me that you'd want to play your favorite character but you wouldn't get to use any of their cards. It's almost like you play with the characters you don't want to play
I'm going to give the game a go using the card of the 5 main characters to see how it plays, but the official rules seem like a strange design choice.