Yes they won the title in 2012-13 but you could tell the empire was crumbling and there was nothing to replace the rotting foundation.
It was just the case of a bunch of olds having one more year left in them. And then once RVP took his customary trip to the training table they were sunk. The prem was also a trash fire that year (WBA 49pts - 8th). For all the talk about LC being the worst champions ever I think they would have beat them in 2 legged tie. In the 4 years prior they had 2 excellent buys (RVP - thanks for the title Arsenal who was only functional for a year, and DeGea who they only managed to keep by dumb luck) and 3 good buys (Smalling, Hernandez - gone, Valencia - now spare parts). With plenty of bad buys (Kagawa, Bebe!, Phil Jones, Obertan etc). LOL Ashley Young was one of their better buys.
I don't think Moyes has been any different, and you make the case that Moyes buys were a lot better than VGs and Jose's. After it was apparent the vets weren't going to play for Moyes the only options were to
-Keep Moyes. clear out all the vets + Rooney and start from scratch with young guys which would have been a 4-5 year plan minimum and if it doesn't work you risk becoming what the RS has turned into.
-get rid of the Moyes. Throw gobs of money around in the hopes of a rapid turnaround.
They chose the 2nd option and it would have worked but its not the 90s-early 00s anymore and world's best wanted to go to City or Chelsea instead. Bale split for RM, Kante went to Chelsea, Mahrez stayed at LC, DiMaria didn't want to go there and played like he didn't want to be there, Marital might be as good as Rom someday. Schweinstiger last year was what Rooney is this year. Its turned into the 4-5 year plan they wanted to avoid under Moyes and they are still at serious risk into becoming what the RS has become. So yea no change. All they have to build around after 4 years is DeGea (if he stays), Rashford (who's game hasn't been picked apart by scouts yet), Marital (work in progress) and maybe Pogba (Fellani has to go if Pogba stays because together that's not going to work).
That being said if the top 8 beats each other up and Ibra has say a 25 goal season they could realisitically finish 2nd-4th. However he's a band-aid, a damn good band-aid but its not going to be a change things in the long run.