That very much depends on how wide or narrow your definition of “mainstream music” is.

For example, Oscar Winning Tears could be considered 'mainstream music " since it’s generally a hit, or not because it didn’t crack the Top 50 of any major market.

Nobody who knows anything about anything and is reasonably sane would, however, consider the vocal display of Raye in the song “unremarkable”…

I wonder if Taylor Swift would have any appeal if she looked average.