Dele is pretty easy to explain tbh.
Young lad breaks into MK Dons team at early age. He is physically more mature than most 16/17yr olds so stands out with his peers and within the lower leagues. As a young lad he plays more first team football than 90% of kids at premier league teams.
He gets his early move to Spurs.
He quickly establishes himself in the Spurs side under Poch. He has the physical attributes to cope with Premier League football even though he is still growing and is really a kid. He becomes a mainstay of the team with the HIGEN press. Dele Alli as he is known then is the pivot of the press. He is the athelete who can cover most ground, is physically capable of putting himself about and mobile enough to get on the end of things. It works really well for 3-4 yrs and he has success with England too.
Now the issues. He was a young man when he came to spurs. He starts to mature. He starts to believe his own hype and starts holding the ball longer than he should and thinking he can be some kind of playmaker. Major major muscle issues hamper him. He was working at 110% without proper recovery or any consideration for what he was doing to his body. He starts to have longer and longer periods out with injury. Poch rushes him back from those injuries and plays him all the time he is available. Its a bad circle which just continues. His last 18mths under Poch he is a disaster. Poch goes.
This all coincides with major family issues. Dele removes any reference to Alli from his shirts. He is surrounded by **** and he starts getting himself into troubles at hotels etc.
Jose comes in as manager (Forget about the other guy). He tries a different approach. The hand on the shoulder doesnt work so Jose tries embarrassing Dele. Dele has NEVER been a good trainer, going in at 50%. He relies on his natural athletisism. Jose turns on him and Dele being a rich, injured, angry young man rebuffs it all. He gets worse and worse. Second season with Jose Dele actually went full pre season abroad with a fitness trainer trying to put everything right. He was absolutely 100% fit. He came back but his game had dissapeared. He had lost all his youthfull energy and was now a man, a strong man but much clumsier.
Dele downfall was Poch & Spurs. But then maybe if he had been held back the inevitable would be him failing anyhow. At least this way he got his time to shine early. Never know but he is paying the physical price of too much too soon imo.