It's foolish to write him off, but it cannot be understated how much of a mammoth task it is to reconcile Spurs' (or Levy's) expectations and ambitions with the reality of their situation.
They want to be a top 4 club playing in the UCL. Ideally win some sort of trophy in the future. However there are 5 clubs ahead of them (City, Arsenal, United, Newcastle) who are in a better position in every meaningful way: better current squad, more money, settled managers. Spurs' position is like Chelsea's, a mismanaged squad and a team outside of Europe trying to get back in it. Yet Chelsea have way more money and in Poch a manager with EPL pedigree.
His task was nowhere near as hard at Celtic. In a 2-team league, he took the team that had won it 8 out of the last 9 times and had to freshen them up for a title challenge. And while he might be able to turn Spurs' fortunes around, the main question is if he will become a victim of Levy before he has time to do that. Arsenal put up with Arteta finishing 8th twice. At Spurs, Levy usually sacks managers who don't look like making top 4. It would be nothing short of an Herculean task to get top 4 from their current state and with the level of competition in this league.