You need it for a CRT shader, but games pretty much universally were in RGB internally and got converted on the way out. Especially for MAME, which is emulating games that would use RGB monitors.
So, there are some exceptions, including a few extremely popular platforms, but certainly you are correct that emulating the majority of game platforms does not need NTSC artifacting.
For arcade, yes, but MAME does do consoles as well in both NTSC and PAL formats. MAME has a pretty high-quality MegaDrive/Genesis driver, for instance.
