Is it feasible for the Switch 2 to have performance near Xbox Series S level at 400$?

[Chrkeller]

No. And to be fair expecting Series S performance from a mobile device is unreasonable, especially one at $400.

Way slower ram, significantly weaker CPU, etc.

It is still a huge jump and 1st party games will look great. 3rd party will be a step behind what is on current generation consoles. How much that matters is a personal opinion.