I don't think Pochettino is a bad coach, but I'm not convinced he's the manager United needs. He has not won any trophies, reached a CL final with Spurs which was good result but didn't excel and although they managed to play good attacking football, their results weren't that consistent.
3 years ago, when Mourinho was sacked, Pochettino was already available. Had the United Board, the Glazers or Woodward wanted to hire him, guess what? That was the ideal time.
But the interim term of Solksjaer was made permanent after his 12 win run and that comeback vs PSG. Now, 3 years later, we can conclude that decision was a waste of time and now are looking to pay-out for a manager that was recently appointed his seat in one of the richest clubs in the world and will overlook other mangers who have more credentials under their names like Zidane, Ten Haag or even Conte when he had no team. Even Rodgers has won more trophies than Poch and with a similar playing style.
Don't get me wrong. I think Mauricio Pochettino is a humble and great manager, and although I do belive he would be able to consistently place United under top 4, I think he would need like 4-5 years of credit to build a team the way he wants and even so, it wouldn't guarantee that it would have sucess. People like Tuchel or Klopp also took time to develop and went blank for some years but their teams seemed to improve overtime in their whole play. I have not seen that with Poch and my conclussion is that there are better options out there.