I think the main point is not how the clubs were performing when he took them over, it's what level were the actual individual members of the squad at, & what budget he had to improve the squads, all in direct correlation to the opposition.
Hes about to compete against 3 of the best teams in the world, with 3 of the best managers in the world, all already well established, plus Man Utd who despite what's gone on recently still have a squad that can beat anyone on their day (& actually should be competing at the top of the table more).
And he'll likely have to do that with less resources than about 4 or 5 teams in the league. Although as an Arsenal fan I'm disappointed Spurs have got a very good manager, I'm actually quite excited to see how he'll get on with this challenge.