Why do you say metagaming? Did he really advance the art so far? I think he was just incredibly good at producing music within his specific parameters.

(Said as a huge fan of his work. I spent a year playing essentially nothing but one of his fugues.)

Yeah he did hugely advance it.

This didn't really get noticed in his own day, as they were busy dumbing things down into the classical period, but he was hugely influencial through rediscovery.

Except for Italian humanists rediscovering Greek and Roman writings, I'm having a hard time thinking of an earlier instance of a chiefly posthumous legacy.