Bugs are related to racerom patch applied to >17 US oem map, so an unpatched rom as his doesn t have problem
i think it s case is that he just doesn t like the tunes he got from those tuners, and maybe the were not objectively well done
oem tunes are very refined under 3000 rpm, and it s very much easy to mess up with smoothess and bogging down at low rpm if you don t spend time to improve it