That's fair but I would like to point out that if we did move Betts, he would be instantly superior to any of these options.
I keep hearing that moving Betts to second would somehow weaken second base defensively. That's pretty laughable. Assuming Pedroia is a nonfactor, which is the only situation in which moving Betts could even bs considered, Nunez is only barely competent at second and Holt is roughly average. They're both reasonable options, especially in the absence of a better option, but if a decision was made to move Betts to second, none of these people are going to be getting in the way of that.
Betts was a pretty decent defensive 2B when he was tried there, although I'm sure he's rusty he ought to be able to get back to the level he showed when he first came up. He's an excellent defender wherever you put him. I get that it would weaken right field, that's what happens when you move an elite player off a position, but I absolutely reject the idea that Betts would struggle defensively at second, there is nothing at all to suggest this other than rust, and rust is a temporary problem.
The primary reason we moved Betts at all is because we had Pedroia. With Pedroia nearing the end of his career the question of whether to move Betts back to his old position is a valid one, at least in my opinion. He would instantly become one of the best second basemen in the league if we did.