The whole issue was quite complicated from my perspective.
First we had the very slow take up of VGA in PC games, this meant the Amiga enjoyed superior graphics for quite a while (up to very early 90s) when the games companies in the EU where still producing EGA games as standard and VGA as a bonus.
Thing is once 256 colour VGA was adopted as default on PC games they were home free. The PC, unlike the Amiga, has just one source of power driving all their games, until much later when 3D accelerator cards became anything like a standard and affordable.
This meant that if you had purchased a copy of any game for your 386 PC, two years later you would be able to see a massive increase in speed just by running it on your new Pentium PC. Win for consumers, win for the programmers. The whole thing is automatic and just a feature of the PC style of computing of that era, which had eventually reaped an advantage once VGA was supported for games.
Now enter AGA, for reasons best known to Commodore they chose to make the 256 colour mode planer...so 8 bit planes needed to be manipulated to generate a single colour out of 256. PCs went for a much more streamlined byte per pixel, this meant one write compared to 8 or so. Instant speed advantage there. How many games automatically improved due to running on an A1200...not many. Did Lotus III get instantly improved to Lotus II levels of speed and smoothness? Nope. Did Street Fighter improve? Nope. Etc etc.
Add to this fact that newer game styles had zero help from the Blitter/Copper duo on even AGA (eg Voxels on flight sims or just plain Doom engines) and were massively helped by the PC's byte per pixel screen arrangement of VGA and the always faster CPU speeds of PCs and you have the whole thing going down hill for the poor Amiga.
There were things C= could have done better, like a special byte/pixel 320x256 mode etc and going for CPU speed upgrade of say 28mhz 68020 on the A1200 for those that wanted it.
But C= had lost its way a long time ago, as well as its bank balance. So in the end it was inevitable I think.