A lot of votes for Kane - which I agree with - but another Tottenham player I'd put forward, for a different reason, is Dele Alli.
I guess a lot depends on what interpretation you put on 'wasting their careers'? Harry Kane is playing really well, at a very high level, but because of that he could be doing it at a club more likely to win trophies.
Up until a couple of years ago, Dele Alli was doing the exact same as Kane and was also linked with big moves. Those moves never materialised and, unlike Kane, he's not kept up that standard and has gone backwards in his career.
Before, he could have earned his move upwards to start winning trophies (as with most being named on here). Now, Alli maybe needs a sideways move to get his career back on track and up to its former level again otherwise he risks 'wasting' it in terms of not reaching his full potential.