Then fortunately, we're having a different conversation.
I've been a loyal Wii U owner since launch, and I honestly don't ever remember it being pitched as the game that would save the system, or any promises of exclusivity (the closest I can think of were vague words along the lines of "no plans to bring it to NX").
The shitty thing to do would have been to abandon the Wii U 18 months ago when it was obvious it wasn't a salvageable system, and move the game to the Switch entirely. Those types of moves have happened plenty of times throughout gaming history.
The fact that Nintendo saw it out with 4 full years of Wii U support and are still giving us this game even though they'd probably be better off putting all their development resources into one basket and using it to drive Switch sales shows that they're committed to supporting their player base, not the opposite. As a Wii U owner that's always seemed clear as day to me. Because my beloved Dreamcast didn't get that kind of support, nor did my Neo Geo Pocket. But Nintendo threw good money after bad on this system for at least 2 years keeping good faith on consumers' investments. I don't know if I'll buy a Switch, but I do know the only reason I'm even considering it is because they did so.