Bitness is irrelevant, just as sprites and tiles are just sprites and tiles, not 8-bit or 16-bit things. Tile layers, like sprites, are rendered by the gpu, which is 16-bit in the PCE. The only real comparative weakness of the PCE vs MD/SFC (single vs multiple tile layers), that youtube commenters and the like often point out as a sign of the system only being "8-bit"... is actually the major 16-bit part of the hardware. Some of the slightly more enlightened PCE detractors sometimes argue that the weak "8-bit" cpu couldn't handle any more than a single tile layer (completely ignoring how powerful the cpu obviously is at running 2D games).
But we don't have to theorize about an alternate reality, we already got a PC Engibe with a second tile layer AND an extra layer of sprites. The cpu is still the same, it still doesn't have any helper chips to offload sound duties like the Genesis and SNES do, and yet SuperGrafx games still toss around a crapload of sprites against overlapping tile layers without slowdown.
Sagaia and Choplifter just do line scrolling/h-sync(?) type stuff. Basically, if there is no reason for dynamic tiles, they almost always aren't used as they take up memory. But lots of SMS and NES ganes do use them. The SMS/GG in particular has some unbelievable stuff. Off the top of my head, the Jungle Book, Lion King, Cyber Shinobi(?), Robocod... there might he a youtube video out there with a lot of parallax examples.
Some NES games with dynamic tile parallax (including transparency) are Bucky O'Hare, Battletoads and that popular Mecha game.
Sonic 2 is one of the Genesis games I remember using dynamic tiles for extra layering.