IIRC the Switch 2 has weaker CPU in exchange for a more powerful GPU compared to the Steam Deck. Considering that console games specifically tend to be more GPU bottlenecked than by CPU, that makes the Switch 2 a bit more future proof since skilled devs will be able to deliver ports with a bit fewer compromises for a bit longer.

But it’s going to take a while before anybody will see the difference in most games, because neither of them will be pushed to their limits in (officially supported) games for a while. Most games that run on the Steam Deck are just running with adjusted graphics settings, not hardware specific tuning.