I think the main thing was that it was ALOT at the same time in the beginning, even with slight guiding through. I wouldn't remove anything from the game directly but would maybe introduce cards / mechanics a bit slower. As you said, it's not a bad thing to start of really slow and get crazier the further you get / longer you play. Especially if there is a very short tutorial type level with limited amount of cards (removing all the fun things or most of them and only focusing on the core elements).