Yup… I have used RGB levels, but not often, and I can’t remember what for. But I don’t think I have ever used Levels.
I have done a midtone adjustment this way, post filmic, a few times, mostly when I’d spent a while getting everything else just right, and only wanted a minor adjustment.
Still, I’m sure it has it’s place in certain workflows - I say this because I’ve thought before “nobody would ever use that” and then discover that there’s a very good use case!