Actually stat guys DO get the value of versatility. When players play good defense in multiple positions, it actually inflates their fWAR values. This is why Ben Zobrist has found himself among the league leaders in fWAR, unless you think he got there by being one of the best players in MLB. ( He didn't.) I have even tried repeatedly (and so far, unsuccessfully) to label the process of inflating fWAR values by playing multiple positions as "Zobristing" and label the players who do it as "Zobristers."
Holt is a good role player for we hat he does,but his skillset is a lot more common than you realize, as there are getting to be quite a few players who play any of 6 or 7 positions. Jurickson Profar has done it. Zobrist certainly has. Arizona has taken to using Chris Owings that way. Martin Prado and Omar Infante both did it before settling in to regular positions. Also Brad Miller in Tampa. And these are just off the top of my head. (And Carlos Santana will be really close tjis year, but that's different because he's pretty awful at nearly all of them.)
Holt really is a weak infielder defensively and a decent outfielder who tends to get hot the less he plays. Sure other teams (notably the injury-prone Nationals) would have loved to get him. But his value probably peaked after his All Star appearance.
He is a good and useful player to have when injuries set in, even mild ones that just require a day off for someone. But the whole idea that he's more valuable to thr Sox is really very silly.
Also I think you might be VERY surprised at how many MLB first basemen started playing that position in the majors. Holt isn't even the only one on the Red Sox. In fact, without trying to figure it out, I would say nearly half of the first basemen in MLB started playing the position after getting to the majors. It's probably the only position like that.
So please stop with the "you never played the game in high school" condescension (which isn't even true). I could go on with the fallacies behind that insult. Or i could ask just how familiar you are with rest of MLB.