The main culprit of the game's technical issues is the engine the game runs on, the CryEngine, not being designed to run on the Wii U.
The game was originally being made for the PS4, Xbox One & PC, but had to be thrown onto the Wii U at the last minute because of a Sonic exclusivity contract SEGA signed with Nintendo & Big Red Button wasn't informed about this until it was too late & they had no time to switch everything over to another game engine that was compatible with the Wii U.
Apparently, the engine's creator, Crytek, tried to help, the developers at Big Red Button, but even they had trouble working with the Wii U's architecture.
It's a real, real, real shame too because if you've played the original FarCry, the Crysis trilogy, Homefront: The Revolution or Hunt: Showdown, you'd know just how stunning & gorgeous CryEngine game's can look when running on the right console or the right PC graphics card.