Defoe's career goals per game for Spurs is 77 in 223 matches, Ade's in the PL is 72 in 163 matches. I guess Ade has probably had more game time but that is not a coincidence.
Given that Defoe does pretty much nothing else for the team other than score goals it is clear who the most valuable player is. To find space for a pure goalscorer in the team he has to be incredibly good at scoring. One goal every three games is nowhere near good enough. Twice that amount puts you in the big league: Jimmy Greaves for example: 220 goals in 321 matches for us. Van Persie has one in two and makes loads more than Defoe. If Defoe is in the top 100 strikers in the world I'd be amazed but he is sufficiently different to do a job as an impact sub.
As far as I am aware, JD is 1st or 2nd in the list of Premier League player to have made a substitute appearance. He shares the top 2 with Kanu if memory serves me correct.
He may only have 77 in 223 matches, but compare actual game time with Adebayor and I bet the stats will be much much more different.
Also, that statistic is a little misleading because there is no control. Adebayor played for a very, very good Arsenal and Manchester City side who will obviously create many chances a game, whereas Defoe has played (not in this spell at Spurs) in front of a pretty poor midfield on some occasions. Last season he had those injuries and very few players come back from injuries all guns ablazing.
Yes, what he did last night in the last minute was selfish, and he should have passed, but I don't think that selfishness can always be used against him. How many times have our players and especially Arsenal been accused of "trying to pass the ball into the net"? A team needs a person that is willing to be selfish and take those chances. Even if he misses a few and becomes frustrating, he will score enough to offset that.