He had an excellent starting eleven full of players that were highly rated even before he joined. At the end of the day what matter is the player that you actually have not the money spent, bags of cash don't play Football. Pochettino is a good coach and helped his players achieve their potential but he didn't do anything that warrants your rating or faith in his unlimited ability to develop. Also he didn't improve significantly during the 6 years spent at Spurs which was the initial point, the point wasn't whehter he is a good coach or not.
On a side note it's worth mentioning that Paul Mitchell was credited as the main influence regarding team building at both Southampton and Tottenham, things went downhill when he left.
By curiosity, do you think that Ole is going to improve in the next decade and reach a new level, he is only 48?
But his squad wasnt better than the big teams he finished over (over a sustained period) and nor was it spending as much. He unlocked the potential in so many of these players to get them at levels that they have nor shown under other managers. Be it Alli, Kane, Sissoko, Dembele, etc.
He also did this at Southampton, he made Fonte and Lovren look really good, and same for Lambert and others. People thought at the time they were quality players, two of whom earned moves to big clubs. He makes these players realize their potential so I find it under appreciation when you say he just had a good team.
The top 5-6 clubs all have good teams with the richest for having most depth. He still over achieved statistically in points and league finish for a sustained period. I find that way more impressive than token cups and the mark of a manager with high potential in the future.
To answer your Ole point - I think he returned to United a better manager to what he was at Cardiff. He said himself he learned from novice mistakes there.
I think Rodgers for example is a better manager today than his early Liverpool days too. He also has spoken of growth as a manager, picking things up at Celtic of possession tactics etc.
And I think Poch will also improve from the level hes shown at Spurs. That improved level from what he already showed will likely be strong pedigree for a big club. Not necessarily Ole though because his level is already quite low as a coach. He just isnt a coach by his own admission, but nonetheless he would improve relative to his younger self over time.