The G3 iMac that came out in this time period had much weaker 3D rendering capability than a contemporary PC gaming video card like a TNT2. Their video ability was closer to the 2D/office oriented video cards sold for non gaming use...
https://en.wikipedia.org/wiki/RIVA_TNT2
Or a voodoo2...
Yes, but Half-Life was designed to be somewhat playable with software rendering even on a 133MHz Pentium and that would have been the better rendering path on the earliest iMacs. In my opinion in that generation Half-Life's software renderer looked better than most of those cards due to the blurry textures and poor scaling (lack of VRAM basically unless you had cash for the 32MB versions) so no big loss for single player play.
To bring up an almost three decade old debate, it would be fascinating to see the performance difference between PPC and x86 in software rendering. Probably mostly bandwidth limited at this point still.
PPC ended up being a brilliant design done mediocre, while x86 is a mediocre design done very well.