Usually, I don't go around sharing advises, but because you've been asking for feedback, here's what I think. My scoring exclusively refers to writing composition.
You have pretty solid composition (the base).
The "Only" thing you need to do is to replace every sound with serious real orchestral instruments, violins, timpani, trumpets, etc.. Also don't forget heavy metal guitars, power chords etc.
But, overall, this theme is little bit too much optimistic and positive for a Final Boss fight.
Yes it should sound epic/winning/positive but not constantly. You should add some dark/scary parts, mix positive and negative, after all it's a clash of positive and negative.
In the future, pay attention to the following.
For example, if the situation is mysterious, the music should sound mysterious, if the situation is aggressive, there is aggressive music, etc. So the point is to adapt the music to the situation. The type of situation dictates the emotion of the music.
This simple but very effective method has been used for centuries, from the theater to the film industry and today in video games. There is probably a professional term for this but I don't know because I'm a self-taught amateur musician. ;)