My opinion is that the Premier League is a very different beast to what it was even 4 years ago. With Chelsea, Liverpool and United all struggling lately it's narrowed the gap to the mid table teams who are now capable of attracting excellent players due to high wages and high fees that they can now afford.
If we look at Tottenham in a bit more detail:
14/15 Stats
Position: 5th
Goals Scored: 58
Goals Conceded: 53
Goal Difference: 5
Jan Vertonghen - 2810mins
Danny Rose - 2371mins
Eric Dier - 2290mins (played CB/RB)
Federico Fazio - 1777mins
Kyle Walker - 1307mins
Younès Kaboul - 990mins
The above defense obviously wasn't working. So Poch decided to bring in Alderweireld to replace Fazio, convert Dier into a DM and bring Wimmer to replace Kaboul. At that point the defense had major surgery and required some time to adjust. So rather than playing expansive football from the start, he allowed his defense to gel. The start of the season for them was disappointing, 5 draws, 1 loss and 4 wins from the opening 10 games. But if you looked at their Achilles heel in 14/15 (the defense) they had conceded 8 goals but scored 16 in 15/16, giving them a GD of +8, promising. It was at that point that Poch allowed Rose and Walker to start pushing forward and by midpoint in the season they'd scored 33 and conceded 15, compared to 14/15 of 24 scored, 24 conceded.
15/16 Stats
Position: 3rd
Goals Scored: 69 (+11)
Goals Conceded: 35 (-18)
Goal Difference: 34 (+29)
When you look at the huge improvement in their defense but then take into consideration their slow start to the season it puts it into perspective that nobody should really be under estimating Spurs. They won't be changing tactics, they won't be changing their first team defense. They'll be a settled first team that can hit the ground running from the opening game. Also if you look at the results against the top teams from last season they are as follows:
Manchester United (A) - 1:0
Leicester City (A) - 1:1
Manchester City (H) - 4:1
Liverpool FC (H) - 0:0
Arsenal FC (A) - 1:1
Chelsea FC (H) - 0:0
Leicester City (H) - 0:1
Manchester City (A) - 1:2
Arsenal FC (H) - 2:2
Liverpool FC (A) - 1:1
Manchester United (H) - 3:0
Chelsea FC (A) - 2:2
Only 2 losses and 1 of them being against us in the opening game of the season. If they are going for the title they need to convert a few more of those into wins. But they're a very difficult team to beat.
The obvious area of improvement is bringing in a player to give Kane cover (Poch seems to have identified Janssen for that). They've replaced Mason with Wanyama who will bring much needed depth to their midfield and the last remaining area of improvement in my opinion is bringing in another attacking danger to play on the right. Lamela is a good work horse and had a good end to the season (4 assists and 2 goals in final 6 games) but they need someone with a consistent goal threat and that's not Lamela. Gotze could provide the answer. I also expect Clinton N'Jie to do well for them, he was unlucky he got badly injured just as he was looking to have settled.