I am sure 99% of you have heard of Hades, Slay The Spire, Monster train, Darkest Dungeon, and other deck building roguelites. They are insanely popular these days. They bring so much of what we like in a game to the table.
Why not set up arena like this? Play till you lose, then obtain rewards for progress.
After x amount of battles, you unlock a trait on a card, or have the card itself increase a level.
Have the AI increase difficulty as you progress.
There are tons of ideas that can be taken from existing games.
That would be something worth playing.
Just a thought.
Edit: I would even play something like that if they charged a sigil for each run.