For sure Quintana is past his best so I think he's trying to make the best of the rest of his career. Nothing wrong with that.
However, IMO, Quintana was insulted having to ride below Valverde during his previous time at Movistar - at least in grand tours. Nairo was one of the few riders who could push Froome at his peak. Examples 2013 and 2015 TdF. AV was never capable of that level. Valverde should have been 2nd fiddle to Quintana in the Movistar pecking order in grand tours.
At Movistar I always had the impression it was a Spanish thing. I was very surprised Quintana went back to that team after how he was treated there. He seemed to get on well with Valverde so it seemed like Unzué was the problem. Quintana's performances were simply a case of cause and effect. Treat a rider badly and they lose motivation. I think he made a career mistake around 2016 deciding to stay with Movistar rather than leave.
I suppose by last year he gave up his aspirations and a return to Movistar was the best option he had.
But it seems he won't be even a remote threat at the Giro. Even wining a stage seems a big stretch. That just reinforces the weak field that Pogacar is up against.
Actually Nairo WAS number 1 at Movistar in the Tour. Regularly.
2013 as a bit of an unknown, he probably started as number 2, made to ride more offensively, anticipating the big attacks, got second. Maybe not attacking on the Pailhères would have saved him some time (on the other hand the anticipation on Ventoux probably helped him) Even as clear number 1 the result wouldn't have been better.
Next year sent to the Giro, ok, you could say that was a mistake, but since in the end he won (stole it from Uran, grrr) it, hard to criticize the decision somehow.
2015 he was the clear leader, he later blamed Valverde (or an unnamed rider that is Valverde) for not winning it. Valverde just not strong enough on the Croix de Fer, Porte too strong, maybe Quintana went a bit too early, that's all.
Quintana was the nr 1 GC rider at Movistar, not Valverde. The constant claim, without any actual examples, that he somehow had to suffer because of Valverde having a higher standing in the team (which he certainly had, but that didn't make him GC leader when Quintana was there) is just BS. Often repeated BS, but that doesn't make it true. Quintana had all the support he could get at Movistar, in the end he was the one who started to fade early suddenly.