I like it. I only like
Holly because it's the name of the plant.
I think it would be cool as a sort of tribute to the
Holly King or something. I don't think it needs to be a specific season though.
I don't think it's a matter of "I love
Holly but I can only use it in December", more "Oh I had a daughter in December. What's a good seasonal name for her? Oh, I know:
Holly!"
Autumn doesn't have to be seasonal either. If the name is common though, like
Autumn,
Holly,
Summer,
May etc., I don't think it has to be associated with that season.
I don't think
Holly is too common.