Splatoon is a successful new IP for Nintendo, in a long time, but on the level of Mario/Zelda? I don't think so.
I'm talking about the fact that Sony's studios are able to make things more successful than their last time and again.
Naughty Dog under Sony went from Jak to Uncharted and followed it up with The Last of Us, each bigger than the last.
Guerrilla Games went from Killzone to Horizon Zero Dawn. Suckerpunch went from Sly Cooper to Infamous to. Ghost of Tsushima.
Nintendo has basically been surviving on the few IPs that put them on the map 2-3 decades ago and have failed to recapture the lightning again since then. Maybe they just don't have the talent anymore or are too scared to invest big money into new IPs, either way they would be nothing without Mario/Zelda/Pokemon. While you can take every IP Sony has and they it wouldn't hurt them any all as they'll make new IPs that are bigger than anything they had.
Splatoon 2 has already outsold at least half of the Zelda games. Not every game sells like Twilight Princess, Ocarina of Time, or Breath of the Wild.