Balancing and hand management and also incomplete explanations are for sure the most obvious issues that are still in the game. They also take a lot of time to test and implement, so we had to make some compromises.
As a short explanation of the "A = B" cards: It basically means get "A scaling with amount of B". For example, Adrenalin Rush does 1 damage at 50 Heartbeat and 4 above 125 Heartbeat.