Even as someone who has a soft spot for Spurs, the more I think about it, the more overrated I think Poch is.
He was DOA until he was forced by the ineptitude of Soldado and Adebayor to accidentally uncover one of the world's best strikers sitting right under his nose. While some of his teammates could already see that Kane should be starting, Poch refused to play him in the league until he had to throw a hail mary to avoid an imminent sacking. His league record was truly dire before he started playing Kane.
Kane's goals saved Poch's job in the latter's first season and he's been cruising at a steady altitude with the elite team he stumbled upon ever since. Kane has rarely, if ever, contributed less than a third of the team's league and overall goals in any given season (more often ~40%). With a newfound goal machine in the team, things were almost bound to improve in the way they did.
Poch effectively took a top 6 team and turned them into a top 4 team. But this event coincided with (and more clearly temporally correlated with) the emergence of Kane, who can make the difference between top 6 and top 4 himself. Note, also, that Spurs' other (future) world class players were themselves experiencing expected improvement simultaneously.
More recently, Poch has had to deal with turbulence in a squad that has been riddled with regression, hasn't continued any natural growth into the players' peaks (having mostly already reached them) and that has lost key and underappreciated players (e.g. Dembele). And he's failed most of these tests with whatever the opposite of flying colours is. As soon as he had to meet serious challenges that couldn't be solved by the players themselves, he began to flag.
Almost all of the variance in the quality of Spurs over the past half-decade or so can be explained by natural variance in the individual quality and intrinsic nature of the squad personnel, which is indicative of a manager who actually has had limited influence over the total quality of his club's football.
He might be good at optimising youth, or at least/more likely giving them a chance, and I get the feeling that he's a good motivator of players who submit to him as leader (which will have grown harder as his stars became world class while he retained his minimal personal pedigree). I see him as a manager with a scattered, restricted collection of positive attributes, notable negatives (e.g. in-game tactics and subs) and a record that is not altogether special when filtered through the lens of external variables: a manager that has more or less performed to par for his entire Spurs career until this year. I believe there exist other managers who could've already won a PL and a CL with the same players.