Skills unlocked at later bosses max-out very easily. Rest of game is perfect. I read some criticisms over low difficulty, but I like the current style. Even the current state of the game would sell on steam. I hope you add more content.
Good point, the late skills are way too cheap. Ember Spirits got slower in 2.1 already, Fire Rain, Molten Hoard and Hydra will follow in the next update. Glad you like the pace, and yes, more content is planned :)