Was the SEGA CD really all that more powerful than the TG-CD? No.
Oh yes it was. Let's look at what it added to the stock Genesis:
12.5 MHz 68000 CPU
PCM audio chip - 8 channels (not 1).
ASIC chip for hardware-generated scaling and rotation of both sprites and backgrounds.
6 megabits o' RAM (Turbo CD was 2 megabits o' RAM).
Thunderstrike used scaling and rotation of sprites and a background layer (all simultaneously). The Genesis could not do this on its own at this magnitude unless it was running at 15 frames per minute. Other Sega CD games that used scaling and rotation are the aforementioned Soul Star, Batman Returns (better scaling than the Neo Geo was capable of), Battlecorpse, The Adventures of Batman and Robin, the bonus rounds in Sonic CD and maybe a couple of others. I agree that Silpheed was FMV generated to look like polygons.
The additional 8 channels of PCM sounded great. They were far more powerful than the ADPCM chip in the Turbo CD. They also sounded much better than the Genesis PCM. Plug in the Sega Classics disc on the Sega CD and listen to the voices in Streets of Rage 1. Now plug in the cartridge and listen to those same voices. Quite a bit of difference in quality!
I fully agree that the Sega CD was not used properly and instead was home to waaaaaay too many FMV games (though Road Avenger kicks all ass). It was also very difficult to program for... look at the mess that is Joe Montana Football CD.