I really wouldn't call any of his seasons a succes at all. Fair play for making top 4 in consecutive years.
The first half season he bottled top 4 by an absolutely terrible run after a great initial run, huge managerial bounce but still he deserves credit for that initial run. PSG was huge, but ultimately reasonably meaningless other than showing character. The football was horrid and embarassing if we are being real.
2nd season was quite awful until Bruno came, he could have easily been sacked after Burnley. Covid seems to have suited us more than any other side for some reason, I don't think Rashford, Mason, Martial, Bruno have been as good ever since but that was a strong 2nd half of the season after the "restart" as well but losing to Sevilla over 2 matches was again really not good enough and an embarassment for the difference in star quality but did a good job to make 3rd, a Leicester total collapse was necessary too. We were still a team miles from City and Liverpool mind.
3rd season, awful start of the season. Had a very bad pre-season due to circumstances, but that start was horrible. United picked up and even came on top, and then came in free-fall again, showing the lack of bottle from the team and manager. Failed in Turkey, and couldnt make it out of the group which is a terrible feat. He got tactically outclassed vs Leipzig, with a far worse team which seemed as the evidence that Ole Gunnar Solskjær isnt good enough if the majority still didn't know it.
Did a decent job in the PL throughout from them to maintain 2nd, toothless against Villareal which was shameful again and worthy of sacking. Not being able to win the EL with that squad is just shameful.
This is without considering the awful cup runs, struggling to get to finals, getting beat by lesser sides whilst the club was desperate for trophies.
He could have lost his job in every season up until this season if he replicated this at Bayern Munich.
Sure some things were positive and there's no point to take away from that, but some were so deluded by this "progress" thing. There was progress in the league finishes yes, but ultimately it was ever far from good enough.
Even during all this time there were periods where we really overperformed our xG, made so much comebacks that was never going to be sustainable, didnt have a clear brand of football or individuals were bailing us out. These things are nice, but not the making of a top team that will challenge for the league or CL which includes teams like Liverpool, City, Bayern, Real, Chelsea (Tuchel).
Most like to act as if it is Ronaldo that has ruined his team and inbalanced everything. Horribly unfair. The signs were there and have been there for a very long time, it was never good enough from Ole, who I think has even done far better than his tactical acumen showing that being a coach is not just about your tactical ability. This season the luck ran out, the expectations were raised (even without raised expectations he should have been sacked this season), and it finally was clear for the strongest Ole-supporter that he just isn't good enough.