Dele under Poch was a fantastic player. Like a lot of Spurs (and England) players, he had quite a serious hangover following the Champions League defeat and the World Cup.
Trippier is a good comparison - had a dreadful season post WC and has been revived abroad.
Dele also only really played under Poch, and clearly struggled to adjust to new leadership. Both Mourinho and Conte are famously abrasive in their styles, neither are especially good with younger players and prefer older experienced players.
I'm resting sceptical about this signing and want us to be a team who offer a home to the younger more dynamic players of Europe rather than washed up top four rejects. Then again the kid is only 25 and, as others have said, his problems seem to be mental rather than technical (Iwobi, I see you).
Got a good feeling.