I agree with you to some extent, but i just can't agree that Switch will become another Wii U: 3rd parties, even if not the big ones, are already onboard with Switch and HW sales - so far - point to that continuing. SW sales of bigger names like Doom, Skyrim, Fifa 18, for exemple, are still a mistery, though.
So, at least, i think it's safe to say Switch will clearly be a few steps above Wii U.
Thing is, there have been only a few big non-port 3rd partiy games - like Fifa 18.
Most of the "great" 3rd party support is based on old ports and so far we really haven't seen a change on that: Activision has been silent; EA has already said their support will be pretty much non-existant; Ubisoft's support has been... standard Ubi support?!
Nintendo, for the first time since GC, has actually executed their strategy of an avalanche of big games to make way for 3rd party developers to follow suit.
But, will that pay off? Most of Nintendo's big names are already out... Pokémon, 2D Mario, Animal Crossing, Smash, are one of the few IPs left to attract a specific userbase.
Wil Nintendo's new IPs have the same impact of a Mario or Zelda? To be confirmed? How will Nintendo manage those remaining IPs (release Schedule) in the years to come? No one knows? What happens if next year there's still no AC, Battlefield, CoD, GTA, RDD 2 (port), Madden, next big IPs sequels?
Switch's success is still not garanteed. And Nintendo still has to prove that they can manage their release schedule (old and new IPs) in a way that not only keeps the momentum, but increases it in the medium and long term.
So, in a sense, Switch can very well become the "little engine that could".