The problem with Neville's viewpoint is that he cites players like Welbeck, Valencia, and Young and thinks them playing would improve United. We know this isn't true because there was a time when Mata wasn't at United and Kagawa wasn't playing yet United were still shit. Plus there were external factors that contribute to the difference in displays. Giggs was involved in the Olympiacos game and his passes were a lot more riskier than what Carrick, Clevershit, and Fellaini are providing. The same with the first leg in the Olympiacos tie. He points to Welbeck changing the dynamic of the team, but forgets to mention that Kagawa entered at the same time as Welbeck. The circumstances weren't the same and it's dishonest to just say that pace was the reason why United were better.
The problem goes beyond team selection right now. There's a lack of cohesiveness among the players. Players don't look comfortable with the ball and do not provide passing options for teammates through their movement off the ball. Those two cause players like Kagawa and Mata to play a lot more safe and pick the ball up from deep spaces. It also causes Valencia to just cross and hit the first defender as we saw in the first half of the season.
I think it stems from Moyes' shit training sessions. There's been a lot of talk that Moyes doesn't do much work on attack or that they aren't efficient in getting the best out of technical players. Many Everton players and staff have said so and there are now articles pointing to United players getting worked up over those shit training sessions.