I think it sounds very happy and not very dramatic and like it could be okay to hear often. I think music for a boss battle should be something youre not alright with hearing all the time.
As a example Megalovania, Spider Dance and Death by Glamour work great as boss music but wouldnt be good battle music. At the same time Rude Buster isnt a good boss theme you need Vapor Buster for that.
I think a boss fight can sound like anything and whats most important is that its tailored for the boss. Maybe try muting boss fights and play regular music over it, it completely changes the vibe and removes the tension of the fight
But thats just a suggestion and what i thought. Other people might feel diffrent