I disagree. I think the job LvG took on was much bigger.
Moyes had the benefit of taking over a team of Champions fully in tact who won the league at a canter, and the mission was to remain in the top 4 as an absolute minimum. LvG had to take over a side that had been mentally obliterated by David Moyes, finishing 7th, a good chunk of the squad were desperate to leave, and the aim was to get back in the top 4!
LvG had to start the refreshing of the squad which Moyes didn't have the balls to do. When Moyes took the job, it needed a little bit of patching up. Perhaps 3 or 4 players from the off, with some players being phased out. But he brought in one to begin with, and it was not the player we needed, nor were any of the older heads phased out. They were first choice right until the end. By the time LvG took over, it needed overhauling.
The two situations were completely different and cannot be compared. But I am certain LvG would not have finished 7th if he had succeeded Sir Alex.
The thing is, everything can be argued either way.
I'd say taking over Sir Alex's champions wasn't a true benefit. This wasn't a regular squad, accustomed to change. This was a squad where a good number of players only knew success under one man.
You then have to factor in that Sir Alex had this team playing functional football for the most part. The mentality was what won them games, in my opinion. A few main men and a handful of grafters.
I don't believe this squad was suited to winning in a more expansive style. They knew how to win by working hard, but not by plying teams off the park consistently. Having this squad dynamic wasn't a benefit, because they foundations weren't built on brilliant football.
You say it needed patching up, but I disagree. I believe the squad needed a complete makeover. Not only did they need the Sir Alex factor shaken out of their systems, but also new players - who had played/won playing better football, with more initiative to attack and create - were needed. Too many of the players in the squad had gotten by (and won) without taking loads of initiative on the pitch. When they were asked to do it, they didn't know how.
van Gaal had the benefit (in my opinion) of being able to make the high number of changes most managers have to wait three or four seasons to make. Most managers are forced, to play players they don't particularly want to play until they have been in the job for a good period of time. He was given the opportunity to do it all very quickly. And there was no resistance, because the last set of players had done poorly.
Edit: also the 'bigger' job is not the same as the rawer deal.