kirby --- genesis = quite a bit more powerful than PC engine. 16-bit processor, with an 8-bit as well (I believe!) so that it could emulate the master system - think that was also in charge of the sound. I MAY be wrong about that, been awhile since I've checked the specs.
PC-Engine - 8-bit processor with a custom graphics chip, actually i think it was 2 separate 8-bit processors or something. anyway that is why you don't see so much parallax (mutlilayered) scrolling background planes in PCE games as you do in Genesis. Interestingly, PCE has a larger color palette than Genesis..
I think atari lynx had a similar scheme like the PCE (two custom 8-bit processors). Also the atari 2600 was 8-bit! yes that measly blocky thing...
one last note, sega genesis' processor was MUCH faster than SNES. SNES was designed as RPGs were becoming the order of the day, so they decided to to trade off processor speed in lieu of prettier graphics (Genesis palette was 512 I think, SNES' was like 32,000?) - after all, in those RPG's, you just crawled arond the screen anyway. So, not so many speedy action games on the system, at least in it's early years. witness the slowdown in games like super rtype, ghouls n ghosts. years later, how they pulled off games like space megaforce (TONS of objects zipping around the screen, flicker-free) is a testament to the abilities of the programmers of the time!