I looked this up to see if it existed and an ability tiering system exists on Smogon, but it's been outdated for three years. I think it would be cool if we could create a community-based one because abilities are really interesting. They are basically the make or break of a Pokemon's potential. For sure, people would use Regigigas if his ability wasn't useless.
I guess it would be unnecessary, but it would be interesting to see where abilities rank with each other, because they really are just as important as the Pokemon itself.
Idk, just something that came to mind.