Put another way - lots of kids have obsessive hobbies. I just read about a girl who got into a college and danced 6 hrs a day. Others do marching band, sports, work, play video games, watch too much tv - whatever.
But everyone owns their grades.
Some schools are stat based. Wouldn’t care if anything was written.
Others are holistic.
Let your passion show. A teacher can write about your passion and dedication in their LOR and your essay can show it.
You’ve made a choice to play piano and it’s gonna benefit you far beyond college. You’ll be playing for your grandkids. I wish I could.
You are who you are and that’s what you go with.
It’ll get you to the right place for you.
Good luck.
PS - there is no evidence that your piano and grades are tied together. None !!!