I haven't seen this week's episode yet, but there was a holodeck of sorts in TAS, so they're not really breaking anything by having one a few years earlier.
As for the swings in tone, TOS had them, too, just not as severe, but watch Balance of Terror (submarine war movie), The Trouble With Tribbles (comedy) and Spectre of the Gun (psychedelic western) and tell me what kind of show it is. I think of SNW as a reaction to DISCO, and maybe an overreaction. SNW was supposed to be episodic, rather then heavily serialized, bright and hopeful rather than dark and grim, and, most of all, fun. It doesn't lean into allegory as much as it probably should to really be a successor to TOS, but I'm happy with it.