I just had a look at the install of ancient NetBSD I have running on my Pocket386, and the X server in there (which is XFree86 3.x) does have a generic VGA driver that does 640x480 at 16 colors just fine. I'm not sure what the "default settings" would be in this context since X that old doesn't even start without a proper XF86Config.
Old would mean mid-90s XFree86.
That's exactly what I'm talking about here, as well. NetBSD 1.2 is from 1996.
320x200 at 256 colors. X doesn't support any depth lower than 8bit, so VGA 640x480 wouldn't work.