Nobody is saying that. The truth is somewhere between 20+ and 6-8 points difference but the uncomfortable truth here is that the most recent squad he assembled was a huge step down from previous Fergie squads and only got across the line because our most important rivals were in transition and continued contributions from fading stars who were still a level above their putative replacements.
I don't buy that it was a "huge step down" from previous squads. It wasn't one of his best (2008 or 1999), but I've seen far worse squads over the past 2 decades. It was a squad that should be finishing third, albeit one that was very top heavy and aging.
Also, our strongest competitor City were not even slightly in transition. They had just won the League and had Toure, Zabaleta, Aguero, Hart, Kompany, Nasri, Silva, Dzeko, Tevez etc. It was arguably the strongest City team they've ever had at their peak; with the added bonus of having the experience of winning the League. We finished 11 points clear of one of the most highly rated expensively assembled teams in Premier League history.
I've said a few times the problem over the last 18 months started with Summer 2013. That should have been a Summer where we spent £150m on 4 key player's quickly, efficiently and in obvious areas. This would have been our new manager putting his stamp on the squad, whilst still having a title winning mentality, title winning experience and a dressing room that should have been together. The fact that we dicked around such that our only signing was Fellaini was utterly criminal.
This compounded the issue this Summer. Instead of needing 3-4 player's on top of the 3-4 we bought the season before, we needed around 5 key first team players (
a winger, a LB, a CB,
2 CM's) and a couple of squad players (RB,
CB). Not only this we needed to integrate essentially half a team into our current squad and make it work almost instantly. To be fair to Van Gaal/Woodward they did exceptionally well to get so many player's in such a short period, of the 7 player's we needed he probably got the bolded. Albeit that the integration part is still hairy at best.
Basically: if someone like Mourinho were hired instead of Moyes, I think we'd have signed 3-4 top player's last season, finished 3rd and signed 3-4 top player's this season and probably been competing for the title. The discussion of how bad Fergie left the squad wouldn't be occurring because dropping 2 places, whilst changing from the greatest manager ever and being back to business the following season would be par for the course.