I think this game has potential to be really fun! I love the concept of starting at max level and having to choose which abilities to downgrade. It naturally makes the game harder without having to completely overwhelm you with enemies. Some feedback:
It was really easy to just pick one or two dump abilities to downgrade all the way (for me, shield and strength). The shield was pretty useless since it stops your movement and allows enemies to surround you and gaining XP is bad, and there weren't ever enough enemies to force me to need to kill my way out to survive. To fix this, maybe try to balance the abilities so there is no obvious weaker ones (maybe make the shield explode out and apply knockback to enemies, and increase the amount of enemies to force you to use the sword), and/or make it so an ability won't show up on the downgrade options if it is several levels below the other ones.
The sword hitbox was really small, and it was really hard to hit enemies without taking tons of damage. With no way to heal (probably? I didn't notice any way of doing so) and gaining XP being bad, it heavily discourages fighting enemies. Perhaps make the sword hitbox larger and add incentives for killing enemies (health drops?). Also, it was pretty difficult to tell when I've actually hit an enemy, so some clear visuals for that would be nice.
Overall, really cool idea for a game. I'd like to see you explore it further!