fifa did it and sold more then 1mio copies on wii in 2007 (ps3 1,7mio in 2007). Thats a big sucsess if you ask me, special because most wii owner werent into fifa before.

yeah. Not only change textures sure but work a little bit more on character models, remove blood and co. It wouldnt be possivle for all games though. I doubt call of duty would work. But assassins creed would be doable

Just another example to make it more clear. 

Assassins creed 4 on wii u should look similar to this in the end

in terms of gameplay, graphics. But same story, world and co as the "big games". 

Splatoon is selling well because it's a Nintendo exclusive with marketing similar to Mario Kart.  Nintendo has consumer trust and brand recognition with their gamers.  3rd parties don't.  Nintendo pushed Splatoon hard because they needed a success.  If 3rd parties need a success, they will push their games hard to their existing fans (on PS or Xbox).  There are no other ways for me to say this too you, so I will leave it at that.

Bayonetta 2's sales are not that far off of Bayonetta 1's sales (670k) vs (910k) vs (1.19m).  It's not bad if you account for how much smaller the userbase is.  

You are comparing multiplat ports (with fanbases established elsewhere) to big exclusives (with fanbases established on Nintendo).  I'm honestly not sure a more faulty comparison could be made.  More apt comparisons:

Batman Arkham City (280K) vs Lego Batman 3 (260K)
Twilight princess  (7.1m) vs Skyward Sword (3.9m)

There is no set rule with cartoony vs realistic graphics and sales.  Sometimes it's appropriate and sometimes it's not.  Making cartoony games will not automatically equal sales.  3rd parties need to develop a consistent brand and consumer trust if they want sales.  It's no different than any other product on the planet.

Make Nintendoish games.

Bayonetta 2 and ZombiU are both overtracked by ~200K each (Bayonetta 2: ~470K, ZombiU: ~650K). Both are pretty much commercial failures. Esiar has the right idea to make 3rd party games successful on Nintendo consoles in general.

What makes you so sure about that? That FIFA was the first game on Wii (and PS3), but since you mentioned sports games...

Madden 08 with realistic graphics ...870k -> Madden 09 "All-Play" (that name should tell you enough)....830k -> Madden 10 (which got WORSE) -> sales dropping every year. 

NBA Live 09 All-Play....220k -> NBA 2k10 with realistic graphics -> 400k. 

but even then those games didnt exactly do well on Wii U either. Hell the PS3 AND 4 version of Rayman Legends sold better. You can make the argument for PS3 having way more consoles, but the 4 version was a late port

you're picking one year out of the many years those systems were on the market? why compare it to PS3 at its worse, lets look at all the years AFTER which are more important. Hell you left out 360 which im sure did better in all versions

Actually releasing the games with no bullshit delays and gimped features is all it takes. the OP is just a hater talking the cliche cartoon graphics.

stop living in your dream and wake up to reality. nintendo always had and always will have the audience for third party games (for all kinds of good games, actually). It's just not possible to buy games that don't exist.