United have been very good all season when the right players were playing. Solskjaer's tactics have been fine but they went into the season completely undercooked squad-wise. Should have got Bruno in the summer. Tactics only count for so much when the players are deficient.
With Pogba, Rashford and Martial playing at the start of the season, they were unlucky against both Palace and Wolves with penalty misses that would have changed the game and probably led to 4 more points. But they played well in the first 3 games of the season. Then they hit a rough patch when a few injuries came in and replacements/squad players just weren't good enough.
Draw against Southampton - Martial is out, Pereira and Mata in attack
Lose against West Ham - Martial and Pogba out, Mata and Pereira in attack
Lose against Newcastle - Wan-Bissaka, Martial and Pogba out, Mata and Pereira in attack
Draw against Villa at home - Pereira, Fred, Mata midfield (lightweight, weak to counters)
I could also have included Daniel James in those. A lot of United's worst form this season was James, Pereira and Mata behind lone striker Rashford. No wonder we were toothless in hindsight. Compare that now to Martial, Rashford and Greenwood with Pogba and Fernandes assisting. Different animal offensively.
I know a lot of teams can go coulda, woulda, shoulda, but United easily could be 10 points better with Bruno taking penalties at the start of the season and being in place of Pereira, Lingard or Mata in several league games.