I do agree with you to an extent. With the league when they were chasing us and then Chelsea I don't really think they 'bottled' the league given that they weren't top at any point and weren't really that close to winning it in either season.
Guess it depends on your definition of 'bottling' though. There's the description you gave above but you could also say that 'bottle' means mental strength in general and I think there's been a few occasions where this Spurs side have displayed a distinct lack of mental strength. You can put it down to superior quality coming through in the end but I think if you put some other teams in the positions they've been in against Juve and earlier today they'd have made a better fist of seeing the job through. The Juventus game they were in a very strong position with 30 minutes of the tie left, up on aggregate and away goals, and they conceded two cheap goals and fell flat. Today they were 1 nil up and looking the better side, and then just fell flat again.
Clearly if you look at the numbers they are overachieving though, can't deny it. They have the lowest net spend and lowest wage bill of the top 6 and they've been beating the other 5 in games regularly and finishing above some of them for the last few years. Fair play for that.
To be honest, I think the way things have panned out has helped them a bit in some ways. They've never really been in a position of massive pressure, like being top with 10 games to go or being 1 nil up in a final with 15 minutes left etc. I'd say the fact that they haven't actually achieved anything tangible has allowed Pochettino and the club to develop the side and squad and go about their business year-on-year without the weight of expectation becoming a burden, and without any reason for egos etc to start spiralling out of control or for them to get above their station. The first couple of years they were almost under the radar and even now they're not the favourites for anything as you say, so they've made incremental progress each season, adding to the squad and practising Pochettino's style of play. It might have panned out very differently if say they had pipped us or Chelsea to the title.