This is a game where you can gain an edge by deeply thinking every turn, counting cards in your deck, figuring out what is still in your draw pile etc. Being able to do these things fast is a skill, just like in chess where lower rated players can also figure out better moves if they are given more itme. But it is not fun to play if you want a quick game but your opponent is taking very long every turn. Sometimes you also just have 10 minutes of free time but there is no telling if your game will last 5 minutes or 40.
I think it would be a great idea to add some time controls to the game, similar to chess, each with their own rating/leaderboard. This gives players more control over how long a game will last if they have limited time, as well as make things more fair in general. Something like a total game time, with an increase to it every time its your turn, and an increase for every time you play a card (ie 1 minute starting time, +10 seconds per turn, +2 seconds per action card played for a quicker game, and 3 minutes, +15s/turn and +5 seconds per action for a slower game, and a much slower, or just untimed, just to give some ideas).