People competing for world first would gladly stack one DPS class/spec if it meant it happened to be the optimal way to play. Making every spec optimal for a world first race is a pipe dream.
The real issue is: are “regular” people actually excluding Outlaw Rogues from progression raids? I somehow doubt it (but feel free to correct me if you’ve got evidence). Outlaw seems to have performed okay throughout BFA:
Patch 8.1: https://www.warcraftlogs.com/zone/statistics/21#region=
Patch 8.1.5: https://www.warcraftlogs.com/zone/statistics/21#
Patch 8.2: https://www.warcraftlogs.com/zone/statistics/21#region=3
Admittedly, Outlaw did fall behind a bit towards the end, but it’s not like Subletly which has been behind this entire expansion. Balancing classes around the extreme minority that’s going for world firsts is not a good idea, I think.
Besides, the changes in SL are not fixing the issue of randomness affecting the DPS. The only way to fix it is to remove RtB.