Di Maria was great until he decided not wanting to play for us. No one could have foresaw that so I would put that down as a coincidence. Think of what we could do with him playing on the left for us right now.
Schweinsteiger was bought to be a leader and offer experience to the team. I mean I don't think anyone thought a 31 year old playing only 28 games prior season and having just won the World Cup would suddenly have the drive and energy become a key player for us. Had he not been injured, I would consider what he did for us as good enough.
Falcao was definitely a disappointment, but it was also a loan. I don't think he was ever brought over to be an essential player in our plan that season.
Pogba however is for sure a key player purchase who is expected to be one of our most important player in the coming years. So far he has been decent, I wouldn't go as far to say a failure. He also didn't lit the league on fire, which many expected a 89m player would. But I don't think that's fair, he's a CM, not striker or winger. Just look at the West Brom game, without him our attacking players look like headless chickens, each trying to do their own cheeky passes, wonder goals or poorly executed crosses. I think Pogba have gotten a lot of unfair criticism just like Carrick did a few years back when people see him side pass and think that's all he does for the team. After our key players from SAF era are gone, we all see him as essential. Not saying they have the same role, but I'm saying their importance to the team is not always obvious to those that don't play or study the sport.
However I do agree many of our acquisitions have been poor. Particularly we've been buying average players for too long. Since SAF last few years we bought the likes of Young, Butner, Fellaini, Blind, Rojo, Darmian, Jones, Smalling, etc. Many of those while aren't terrible, yet we desperately needed better. So I don't think the big names we bought were poor, rather the other transfers we got were poor. That I think is the bigger culprit to our poor results since Moyes. The fact that we bought Martial - a teenage striker, just to play him as a winger shown how poor some of these transfers are. With RVP, Rooney, Falcao, and Zlatan, Martial were never going to get to play as striker and he's unfortunately not a winger either. He can't cross, he hasn't got the best dribble, he's not a great passer with great vision, and he's not going to fashion much chances for others because of that. Right now all he does is side pass or try forcing his way into the box. While useful, it's too one dimensional and slow. Furthermore, we're forced to shove him to the flanks because we do want to play him, but we have no where else to put him. Rashford is suffering the same problem and so far this season neither of them have actually fit into our system and offer the team what we really needed on the pitch. I don't know what Jose's plans are for next season, but if we are going to keep Martial and Rashford, and genuinely want to play them because they have potential, we need to play a formation that can fit both Zlatan and Martial/Rashford in it. Otherwise they're just going to be backups for Zlatan, Mata, Mhki, and potentially Griezzmann or similar caliber player. Which is fine by the way. But that's my whole point. It's not that our galactico signings haven't pay off, but that we don't have enough of them and are actually fielding too many average players around the few that we got.