There are a lot of things to criticise LVG for, but to say LVG was not good in big games is going a bit far as overall his record was very good, with the odd blip. Going into the games against the big 6, I went from thinking the game was lost before it was played under Moyes, to thinking we could get a result with a chance under LVG.
Top of the "Big 6" mini league in both seasons and isn't that often teams get 18+ points - in fact I remember someone saying that winning home games and drawing away games against the big 6 (so 20 points total) should be enough to win the league as long as you do the business against the lower teams. 18 points is respectable but his record against the lower teams was dreadful and that (along with the many goalless draws, lack of shots, poor record in CL etc) is where the ire should be.
Van Gaal isn't a United fan. I doubt he watches many of our games except for the big games, so if he's on about purely them he might have a point but overall Jose is much better.
This season we're on track to having a "points v big 6" record like we're used to. Our points vs the rest of the table on the whole is great - with the odd blip like Huddersfield - just sucks that we're against this City side.