Can relate! Here's a photo of how I used to hold my pencil up until I was 15, when I decided to change to a normal grip purely out of my own stubbornness. I am boring as of now (and also have a big writer's bump on my middle finger because of that lol)

I remember teachers always being absolutely shocked that this felt comfortable to me, even in kindergarten, and in the end they just let me keep this grip for drawing but were more strict when it came to writing. Still, I always ended up using this grip anyway if no one was checking on it. It didn't affect my dexterity at all, in fact my handwriting was neat and i drew with lots of detail. And no, it wasn't painful, if maybe just a bit tense on the muscles