In terms of signing players who made a positive contribution to the club after the manager who signed them left then Moyes > Van Gaal. The latter only has Martial to show for his time here, despite presiding over many more transfer windows and spending a shit-load more money than Moyes. Along with a bunch of flops.
Moyes left us Mata and Fellaini, who have both been useful players. I actually don’t think he signed any complete flops at all? He got a lot of shit for being “dithering Dave” about transfers but I would argue that’s a lot less damaging to the club than spending huge sums of money on players that aren’t good enough or don’t fit. Ditto re prematurely sacking off players who might have been useful squad members (e.g. the subject of this thread).
Well i am sceptical the Mata signing was Moyes idea, and despite liking him as a player he hasn't been a great player for United in my opinion. In some ways i think he has held us back from getting a proper right winger. Van Gaal also signed Herrera who has been a good player for United and Blind and Romero have both been good servants. I would actually rate Blind alongside Mata in terms of contribution.
Setting the signings comparisons aside i don't disagree that Van Gaal did massive damage to United, damage that Mourinho is still trying to fix.
But i still don't see how Moyes is being excused here, everything that has happened to the club since 2013 was set in motion by Moyes and his complete incompetence. Even setting aside the disastrous on pitch performances, he set the foundations for the clusterfeck that Van Gaal made of the squad.
In 2013 the squad that Ferguson had already let get past it's sell by date (understandably) needed key additions. Moyes didn't provide them, and no i don't think Fellaini or Mata solved any of the key problems back then. By 2014 not only were we a few years behind in rebuilding the squad because of Moyes we were also losing the experience of Evra, Vidic, Ferdinand, Giggs etc. all in one go. Players Moyes should have at least partly replaced.
He left a mess for Van Gaal and yes Van Gaal made it much worse through his own crazy decisions. But Moyes still did massive damage to the club in his season. As i said earlier everyone can have their own view on just how much damage each manager did during their respective tenures. But to suggest Moyes didn't do much or even worse no damage is nonsense in my opinion. People hate LVG and i can understand why, but that shouldn't lead to them rewriting history and absolving Moyes of his share of responsibility for United's current predicament just to heap more criticism on Van Gaal.