I would guess its much more subtle than this. Consider potentially nintendo refusing to port games that were on steam, or demanding more money/control over games that have overlap with steam.
Punishing publishers for choosing to release on a competitors platform they don't like would hurt those publishers more than Valve. Nintendo's relationship with third parties is already often strained, doing anything like you suggest would in particular cause indies, which Switch relies on to fill the gaps between Nintendo releases, to flee the platform.