As it has been mentioned, 3rd party sales on the Switch have not been bad at all ( I remember reading about the Witcher 3 port that was 4 years late selling 2 million or so). With that being said, I don't think ( at least at first) sales could reach the level found on Sony's systems even if the versions were the exact same and came at the exact same time simply because Nintendo's ecosystem is just not the same.
---Member of the official Squeezol Fanclub---