This is a pretty fun build for ~2 hours of work!
What led to the decision of having the deck building be random?
This was for a Low-Effort Game Jam; so complete randomness made things easy to program lazily for the idea to still work.
And for rock-paper-scissors...it's a weird game system. Playing against your opponent purely randomly will get you to a 50% win rate. In order to play best against your opponent, you would want to put together a deck which has a perfect balance of all 3 card types, so you can respond to any card that gets played. By only showing 2 at a time, you have to keep track in your head about the cards you've picked to get the best balance possible, it's the only actual challenge in the game experience.