My take.
For those peak Poch years Dele was one of my favourites, an instinctive player with no little amount of skill and passion for the shirt. His decline from 2018 onwards has been startling but went hand in hand with that of the team. Though it is worth noting that his 3 partners in crime, Kane, Son and Eriksen did generally maintain their level of performance, whilst he did not. He morphed into the most frustrating player I can remember at Spurs in years.
I don't agree with the narrative that he lost his desire, was more interested in tiktok and was just going through the motions. I always felt he was trying, although maybe he did become a touch complacent in Poch's final 18 months as he would always be selected regardless of form.
I also don't buy the other easy narrative that Mourinho (taco that he is) ruined him. Jose saw an underperforming star player and tried the only technique he knows. Tough love. It didn't work but he had to try something because Dele's career was stalling at that point. To me his form since then has been no better or worse than before Mourinho turned up.
For me, it's just that he seemed to stop doing even the basics right and when the ball came his way 9 times out of 10 he would either flick it nobody or slowly dribble into a defender or two who would take the ball off of him with the minimum of fuss. He became the rocks on which too many of our attacks floundered.
It is a great shame and a bit of a mystery as he had the footballing World at his feet, but as others have said, even peak Dele would struggle to have a role to play in Conte's preferred system. So it's right that he has been allowed to leave to try to reboot his career at Everton.
Will he suceed?...who knows, but I wish him luck.