"Oh no! Big crash on the back straightaway takes out William Byron, Kyle Busch, and Harrison burton!"
Normal liveries are hand-crafted by the BSC team specifically for this mod, are very accurate, and are very high quality; the MSG liveries were imported by DriveThrough and while they are also quite accurate, the importing process does affect the quality of some of them. Notably, slightly altered colors and compression are notable on a good portion of the imported MSG schemes (particularly noticeable in the 4k pack). The MSG pack, however, does have more schemes available than the set created by the BSC team.
Tbh, if you don’t want to read through the forum for info, and clearly didn’t take a moment to look in the parts menu for the skins (you’d been asking for a few days), just to come back and demand someone be polite and helpful to you because you didn’t bother looking for them, sounds like a you problem if you think Owlkitty was being rude.