There’s a simple truth about the modern game: unless you are prepared to put a shift in, both in training, and on the pitch, then you’re going to get found out. Perhaps this wasn’t the case in the 70s, but with current ubiquitous fitness levels and monitoring of players, it’s a must in today’s game, certainly at the very top. The money in this part of the game dictates that to be so.
If you don’t want it enough, either through a love of the game, or the money that flows through it and associated respect for the contract that provides it, then you’ll get found out quickly enough.
Raw talent will only take you so far, and for so long. You’ve got to want it enough, and Alli plainly doesn’t.