Honestly I think the OP is a false premise to begin with. Basically I think there is this (false) belief that somehow by supporting your previous system well it means your next system will do well because of brand loyalty or something.
But it's really not true if you actually look at it. In fact, the most successful modern Nintendo systems and the most successful Microsoft console all stem from those companies prematurely killing off the preceding system.
The DS was a massive success after Nintendo prematurely killed off the GBA.
You're strawmanning the original post. He's not saying that supporting it would mean the next console would do well too, so it's pointless to argue against that point and pretend you're defeating his post. He's asking what people think about the suggestion that the Wii might have been a better console to get behind than the Wii U in terms of profitability potential.
Your conclusion doesn't examine the facts correctly, either. The Wii and Switch were NOT popular because of prematurely killing off the Gamecube and Wii U, they were popular because they were compelling hardware with killer apps. It would be more accurate to say Gamecube and Wii U were dead/near dead on arrival, neither console was ever very popular.
And the DS was a massive success quite a while BEFORE Nintendo killed the GBA off - that's not premature. Nintendo heavily supported the GBA for about two years after the DS launch releasing some of its best games in this period. Many major franchises released on the system in holidays 2004 through 2006 including: Mario, Zelda, Pokemon, Donkey Kong, Fire Emblem, Final Fantasy, Harvest Moon, Mega Man, Yoshi, and Wario. Additionally, Nintendo released two new hardware revisions of the GBA (GBA Micro and Backlit GBA SP) after the DS came out.
I describe myself as a little dose of toxic masculinity.