The PC Engine / Turbo GrafX-16 has two 8-bit processors running in parallel, does it not? That is why it is considered 16-bit, yes?
That's a myth as old as the console wars.
The "16-bit" generation got its name from Sega putting a large 16-BIT decoration on the Mega Drive. Before that, no one talked about bits at all.
The "bits" of a cpu isn't a measure of its performance, but even if it was it is still only one part of a console's hardware. The PC Engine's single cpu is "8-bit", but it handles 2D games better than competing 16-bit generation consoles.
The 16-bit graphics chip and the overall hardware design of the PC Engine also makes it the best at animating background tiles and especially sprites. A game like Sapphire shows how the cpu can handle Neo Geo game levels of sprites/action/animation, even with 2-player co-op, without slowing down. You'll notice that PC Engine games tend to have a variety of shapes and sizes of sprites, while SNES games have oddly proportioned sprites and minimal variety, similar to NES games.
The PC Engine has the most potential for color/shading/detail by having 8 times as many palettes as Genesis and twice as many as SNES, but this is the most underused hardware strength in the existing library.
Overall, the Genesis and PC Engine are comparable at handling a lot of action and variety, with the SNES far behind and closer to Sega Master System/Game Gear. Each console has strengths/weakness and trade-offs, with the SNES being the one with the most trade-offs.
In the end the PC Engine and its games are closest to other consoles that are grouped under the moniker of the "16-bit generation".