"My confusion was that I thought once a card was played it was removed from the players deck permanently. (Did I miss it? Was there an explanation in the tutorial that at the end of the level the cards are returned to the player deck for the next round?). "
That's a good point, I should explain that better in the tutorial. I'll add a line or two about it.
"Does the Genius & Alpha card take all the points from the rival cards immediately? That's a major buff when there are 3 rival cards in play - maybe make it a slower drain?"
Yes, they do take it immediately upon entering the field. All effects that happen at the start of the turn are like that. Maybe I should change that so that all start of the turn effects don't happen in the turn a new rival enters the field and only in the next turn. That actually might make the game more fair because it gives the player time to prepare.
I'll also change the Genius/Alpha effects so that they only take points from 1 other rival card per turn and not from 2. This will not make a huge difference, but it's another way to give the player a little more time to react in certain situations.
"Now that I understand the rules better, there seem to only be a few unwinnable scenarios in later levels."
The goal is to make it as skill based as possible. There will always be some RNG, but the goal is that a good player than understands the mechanics can beat later levels consistently with different strategies, but a less skilled player will lose earlier more often. I think you're already seeing that there are less unwinnable scenarios than you first thought (and they might be even less than that, because you might have made bad plays those times you lost, meaning it was actually possible to win).
My job as game dev is to try to reduce those unwinnable scenarios as much as possible, so that your choices as a player really matter to win or lose!
Thanks again for the feedback, suggestions.