Or we could just generate our own version of RA9 WAR that accounts for specific defense behind a player instead of abandoning the concept.

The biggest problem with rWAR is that it's not even measuring actual defensive outcomes, it's estimating it based on team seasonal defensive stats.

Miley had -3 OAA and Burnes and -5 in 163 and 202 innings

or - 1/6th of a run per game versus versus 1/5th of a run per game for Burnes.

you can literally just plug those into rWAR's pitcher formula and generate a revised RA-9 WAR that doesn't just pretend defense isn't a relevant aspect to adjust for.