I think there are 2 times to truly evaluate a trade. At the time it is made and 2/4 years later. At the time this was made, if Varsho is a consistent 5 WAR player you can squint and see it make sense. But he crashed to 2.1 (same as LGJ). Moreno just turned 23 and was a top MLB prospect in a premium position that has +2 years control.
Players can press hard after a trade and do worse or they can get a new team (the good ol' change of scenery narrative) and take off. I don't think there is any hard evidence thats supports anything conclusive in this area. You can point to examples of both cases easily across MLB. Putting Varsho in the 4 hole to start in the year, in retrospect, probably wasnt the wisest move for his confidence.
I think most of would have rather moved Kirk but maybe that didn't get the trade done or our FO wanted to keep Kirk. We will never really know.
I see the point you are trying to make but I dont know that the Scheider reference is logic analogous. Varsho is 27 already with 1600 PAs (3 full seasons) career 96 wRC+. Looks like more than a sophomore slump. Looks like this year was closer to to who he is at the plate than '22. His savant page is ugly offensively. He did hit a ball 113 this yr so the upside power tool is real. He just didn't do it enough.
Could he be another Jose, Edwin and JD who improved their offensive numbers later in their careers? Yep. But thats hunting unicorns. I'd say there is just as much chance his D falls off as he ages. His sprint speed is 69th. His arm is 40th percentile. His jumps and reads are excellent. His D has to be elite to add value. I am looking forward to seeing him in CF all of '24 to see how he reacts, and if he can bounce back to a league avg or better bat. That would take him back up to 3-4 WAR and this trade would look better.