There is slight downgrading and there is significant downgrading.
No one wanted to develop for wii u because they didn't want to make games in mind for PS4 only to significantly downgrade for wii u.
That wasn't the actual reason though. It's really easy to lower the quality of games. Otherwise most console games wouldn't even exist.
The thing about different machines is that they come with different features and with those different features, you need to code things differently. Hence why No Man's Sky barely worked on PC at launch, because they failed to understand that part.
There was something about the Wii U's hardware that wasn't too friendly for third party developers, but seeing how I don't know much on the subject, I wont touch up on that. Nor will I throw out random stuff like someone else might, and believe that random stuff I'm not going to spew.
The Switch however, uses hardware many developers are already accustomed to, hence that partnership image that keeps floating around.
And even with all that, the Wii U still did good. Splatoon and Smash were pretty popular games, if not still are.
