It would have killed nintendo to add an ethernet port. As someone who bought the dongle, having a wired connection will NOT save you from nintendo online being the worst gaming networking service ever devised. No game benefits from it, least of all actual nintendo titles like splatoon or smash. It's not even a problem of speed, it's wholesale reliability issues, constant loss of connection errors. If an ethernet port was available included rather than needing to be a seperate purchase, more people would realize sooner just how truly awful the paid nintendo online service is.
I'm just still mad that I could play phantasy star online for ten hours uninterrupted on my gamecube, but now there's not a single nintendo title that has stable online. Pokémon might let you get a raid or two before needing to reconnect. Splatoon might get a match or three before needing to reconnect completely. Smash won't stay stable for even one full match. It's a complete tragedy.