Lol at Souls simply untrue, DS1/DS2/DS3/Sekiro/Elden Ring/Lords of the Fallen/Lies of P/Armored Core VI etc completionist here all on kb/m. I can obviously control the camera a lot better with a mouse which is a large benefit.
Really unless all those people are playing racing games or fighting games they're doing it wrong, kb/m is always superior otherwise. I use kb for racing too anyway even though I do think a controller would be better, everything from NFS to GRID to DiRT to Horizon, probably will continue to until I have a wheel one day, still gets the job done just have to feather the keys. Hell I played the last three Devil May Cry games with kb/m. I grew up with consoles first (and played Demon's Souls first on PS3 as well as my first playthrough of DS1) and still own one, but there's no substitute for a keyboard and mouse straight up.