Are you trying to say they every played as beautiful or dominant as Ten Hag Ajax? That's simply not true. Yes, Poch had a very good season that year, but it was nothing out of the ordinary. Let's not forget that Chelsea's Conte won that year. For all the praise you seem to be giving him, he won nothing that year.
Up and coming is important because you need managers who are at the top of their game, not past it. For example, maybe if we took Mourinho after Inter or even after Real Madrid, he might have established a successor dynasty of Fergie. Instead we took him after the Chelsea meltdown where there were obvious signs of his decline and suffered as a result. It's a similar case with Poch - we should have gone for him after he got sacked by Tottenham, now we're going for him after his less than succcessful stint at PSG were he appears to be cracking himself. Not gonna work.
Okay, I find this argument to be a bit of a nonsense and I don't know why it keeps getting repeated. Which top manager has ever needed "experience" in order to be in charge of a big club? Did Zidane need an experience to be successful at Madrid? Did Simeone need experience to be successful at Atletico? Did Pep need experience before being put in charge of Barca? Or Flick at Bayern? Top managers are top managers, they do not "experience", they need "IT" Ole didn't fail because he didn't have experience at a top club, nor did Moyes, Mourinho and LVG succeed because of their experience. They were simply not good enough.
This "experience" thing you talk about - by the time Ten Hag gets it, he'll already be snapped by a top club, become unavailable to us and then once again we're going to be be searching for "experience" and miserably failing with every supposedly "experienced manager" while the so called hipster choices make us look dumb. How long before we realize this simple fact that United is not special? This club isn't above the others for managers to prove themselves at City, Liverpool, Real Madrid, Barca, etc before they are graced by the opportunity of working as a United manager.
I also want to say that literally every single manager is a risk, even Pep and Klopp. Pochettino is a huge risk himself - there is zero guarantee that he will succeed or even get us top 4 on a regular basis. Ten Hag is a risk, as well, but he is a risk with very high reward potential. People like yourself were the same ones that argued Pep and Klopp were a risk