Generic VGA doesn't generally exist on EFI platforms, the firmware doesn't program the card into a state where the VGA registers are going to do anything useful. You should get a working unaccelerated framebuffer from the firmware, though.

Not only that, I remember X.org source tree had a bult-in x86 emulator so VGA bios of some PCI video cards could be run on Solaris.

Technically not related to Solaris, since Solaris x86 existed and you wouldn't need it there, but yes, this was used on Sparc and any other CPU unable to run the card BIOS (including 64-bit x86 Linux, since virtual 8086 mode goes away when you're on long mode)

I remember the "generic" VGA driver having horrible default settings that resulted in 300x200 at 16 colors.

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.

X absolutely supports depths of 1 and 4 bits per pixel, along with 8bpp, with its VGA server: https://www.xfree86.org/4.8.0/vga.4.html

Thanks for the correction.

I hadn't thought of 1bpp because it isn't interesting on VGA hardware. But you're absolutely right about 4bpp having been a thing.

X does, modern X apps may not.

I remember that Xfree86 allowed 1 bit (B&W) modes