Rangnick apparently lost the confidence of the dressing room because the players thought he was too indecisive. He kept waiting for his analyst in Russia to talk to Armas through his earpiece before making changes to the game. He simply wasn't a football manager. It was ridiculous.
Ole was never a great manager either. But at least he got the basics right in his first two seasons and built a decent atmosphere in the squad during that time. He inherited Mourinho's counter-attacking team and did a good job of reinvigorating them with the confidence to continue playing that way. People criticise him for being all about 'vibes' but if 'vibes' were really that easy, everyone would be doing it. Unfortunately, he wasn't good enough to lead the transition from counter-attacking to possession-based tactics. But anybody who's managed a group of people will tell you that training a new way of working isn't the difficult part; the difficult part is convincing your team that it's worth doing. In that regard, Ole was let down by Woodward and Judge creating a bloated squad of underachievers who became impossible to convince of anything. The board overpaid and undelivered on new signings, and extended the contracts of every bad apple in the barrel.
In the end, neither manager was top class. This season was an almost impossible job for either of them given the imbalances they were given in the dressing room. But Rangnick knew the job going into it and couldn't even manage the team on a match day. On the other hand, Ole at least showed he could get the team playing well before the squad was sabotaged underneath him. Overall, Rangick was clearly worse at delivering on his remit.
