Yea, I could also blame steam's SD verification system, which just rates compatibility without giving much thought to performance. Cause I'm aware BG3 "works" on SD but walk into an area crowded with NPCs and it becomes an impressionist painting at 10fps
ProtonDB is better for gauging the performance penalty, giving different "medals" in accordance with how good/easily it runs on Linux: https://www.protondb.com/
