Thanks for your great feedback, I'll try my best to not create many excuses as possible.
The UI is so junky and I agree with you in that regard, I did not tested it on an actual itch.io page, so it had a lot of problems, it was also too basic and not as good as I thought it would be.
For the CPU, it's actually picking every possible action and choosing one of them randomly, hence it's extremely suicidal, however it is switched to a more smart and very agressive version after the 3rd level, and I took that design decision in order to make it easier for players to farm some summoning cards and skills before facing a "tough" opponent, it's definitely not the best design choice but it was all I had at the time.
I'm definitely gonna improve the demo once the jam is finished so saty tuned for that.
And thanks for your detailed feedback it was really informative.