Earlier machines, 386s and Quadras were a joke compared to Amigas (1200 and 4000).
Theoretically there was no difference as you could, ideally, just rewrite your renderer to render in planar modes directly instead of rendering to chunky (per-pixel) modes and then converting to planar. And chunky-to-planar converters eventually became quite fast but it was too late and nevertheless an overhead.
Amiga did quite fine until 3D graphics. "Modern" games like Dune 2, Syndicate, UFO: Enemy Unknown, Settlers, etc. were hugely popular but still complex games, yet playable, and no less good looking on Amiga than on PC. But then Wolfenstein, Doom, Descent, and others with full-screen 3D graphics with texture mapping happened and Amiga just couldn't even start the race.
If Amiga had had a chunky graphics mode it would've certainly had a few more years until complete technical obsolence. Commodore basically had that chance with Amiga 1200 with the new AGA graphics chip but they chose to extend bitmap planes instead.
For anything else, Amiga was competitive despite the lack of cpu power. I remember the last years of my personal Amiga use. Productivity software, editors, programming etc were still snappier and a much more friendly experience on the Amiga even if PCs at the time had 10x the cpu speed and Windows software was maturing up (and subsequently getting bloated beyond all usability).
"Hunter"[1] which was flat shaded 3D, had a very large play area of multiple islands and had multiple drivable vehicles, you could ride bikes, row boats, gunboats, jeeps, tanks, helicopters, surf boards, hovercrafts. All on an Amiga 500, all on 1 floppy disk.
"Mercenary 3" [2] also flat shaded, had a fully simulated solar system with day/night cycles. You could go in buildings, go in taxis, get on a space ship fly up to orbit, go to another planet, land in the city go in a building. The scale of this game is insane for the time.
[1] https://i.ytimg.com/vi/MzByYlnvaN0/hqdefault.jpg
[2] https://www.myabandonware.com/media/screenshots/m/mercenary-...
Amiga could certainly do vector graphics but without texturing. The Blitter chip could easily fill large areas with the same color.
Hunter was an older game still but for example Frontier (Elite II) was also more than playable on Amiga and it was a "late" game, around the time where texture mapping was already getting common on PCs. A bit earlier F1GP offered very competitive detail at the time, again with non-shaded polygons only (you would get some textures in the PC version).
Not so much Amiga wasn't as fast as PC at the time, but rather something with the bitplane based graphics system not being suited for the psuedo 3D kind of games.
Amiga coders compensated for this with very fast, insanely optimized assembler code. They were so good that a multiple times computationally slower Motorola processor would run a Doom clone at the speed comparable to a contemporary PC bucket.
Never.
You just could not get a VGA-on-i486 level rendering performance out of 256-color AGA fullscreen, even with Motorola 68040 on the Amiga 4000.
All the fast 3D demos and games I saw were partial-screen, with 2x2 pixels, or both. Good-looking ones were slow. An example with at least some commercial success was Alien Breed 3D. Check the video here: https://www.youtube.com/watch?v=ksQG8vnvlpg
Because it was so hard to do per-pixel rendering on Amiga all these 3D graphics demos and games on Amiga basically concentrated on delivering the graphics only, with shallow content and amateur-grade playability. Doom had a lot else going on despite the smooth graphics, and that actually made Doom a good game.