Getting back into the swing of things, I see?
I’m sorry, the opportunity was too golden. Anyways, my opinion of this song instantly shifted when I heard you describe it as a jazzy battle theme. At first listen, I was unsure because I was expecting even more emphasis on the swing background harmony than what there was, and perhaps a harmonica to bring that feeling home. However, this uses brass more than those classic instruments, which implies a grandiose feeling associated with a boss fight. Two main issues with this song, despite how catchy it is:
1. The intro. Having JUST piano for like the first 1:09 gets a little repetitive. You mentioned this in the description, but this is repetition based on lack of variety rather than repetition of melody (I think you were right that the melody works well for the feeling of the song).
2. The outro, although this one is more of a personal taste than a real issue; the fakeout ending didn’t quite work for me, although I do appreciate you trying something new. My main hypothesis for his might be the fact that the piano at 2:45 just replays the same six notes as the melody at 2:43, just adding another measure to the melodic phrase. It might have been more satisfying if you instead just finished the phrase with those six notes instead of playing them twice. Anyways that’s really honestly a huge nitpick and, so you’ll still get the five stars for taking a well established type of music and putting your own spin on it in a fleshed out way.