The clip posted on this page kinda highlights why I find a lot of the current talk about Rangnick here a bit over the top. The beginning of that clip, he is using Liverpool as a comparison, and talking about how the most important is figuring out how you want to play and starting from that basis. Hire a manager, get the right players in, etc.
In Liverpool's first full season under Klopp, they brought in Mane, Matip, Wijnaldum, Karius, and Klavan. That's five transfers. Three were succesful, two were not. Young-ish, hungry players that fit the manager's ideas. In comparison, Manchester United have hired Ten Hag. They have looked at signing players that fit Ten Hag's style of play. Three signings have been made: Eriksen, Malacia, Martinez. They have been chasing De Jong and were probably hoping to have him. That's four players. Three of them are young-ish; Eriksen is the only outlier, being a weird market opportunity due to his health scare. Liverpool lost a lot of players that summer. So have United.
What United are doing isn't dramatically different than what Liverpool did, which is what Rangnick said they should do. Liverpool, I should note, began that season with a 3-4 win at Arsenal and then a 2-0 defeat to Burnley. This is with a manager who'd already been there almost a year, mind you. Ten Hag just started.
United have spent too much time on the pursuit of De Jong, which signals various problems at the club, but this is a problem of execution, not strategy. Could Rangnick have helped with execution? Maybe. Probably not as a consultant, but as far as his skill set goes, sure.
I don't think it's justifiable to act like the club are doing the exact opposite of what Rangnick wanted.