Tell me, could you buy Mark of the Wolves for Neo-Geo at Babbages upon release? Or whatever it's 1999 equivalent would be? Or any retail store in the US for that matter?
If the answer is no, then that further drives the point home that at some point, Neo Geo games don't qualify as 16-bit anymore, even they run on "16-bit" hardware. Look at it this way, a Neo Geo game has to have been at the very least released during the lifetime of actual 16-bit home consoles, and maybe even be ported to those systems. When Metal Slug came out in 1996, the 16-bit market was dead and the 32-bit generation was already well underway. Metal Slug was ported to the Saturn and was available on Neo Geo CD. That means Metal Slug was a 5th generation arcade game.
Yes, it's cool that such an old piece of hardware could be capable of playing such new games, but that isn't a reason to compare Mark of the Wolves to a primitive port of Street Fighter 2 on the SNES. It just doesn't make sense.
Besides, the Neo Geo's capability of running such high end games is really quite simple. The system's huge cartridge bus, allowing for a very high ceiling of ROM space, added onto the system's basic hardware features, equals games like Mark of the Wolves and Last Blade 2. Much like any cartridge system, the ROM space, compression, bank switching and other data management tricks amplify the system's basic and advanced hardware features. A late game like Ristar on the Genesis is honestly quite impressive compared to Space Harrier II, an early release. The reason Ristar is so much more advanced is due to more ROM space and better use of the Genesis hardware. Both Space Harrier II and Ristar run on the same exact hardware.
Yes, it's 16-bit. If it wasn't, then the Genesis would also be 24-bit, seeing how it also has a 68000 and a Z80.
Fun fact: Early models and revisions of the Neo Geo (arcade and home) hardware used a regular Z80 instead of the Z80A. Those units today are known to suffer prematurely failing Z80 chips, because SNK would clock Z80 up to the speed of the Z80A.

