I feel for Dele, but let's not blow it out of proportion. He's not abnormal, he's just had an abnormal trajectory.
I'm not sure ALL players know when they've had a stinker. It's common to see players complain when they have nothing to complain about.
Also, it's an entertainment industry. If someone is coming on in the wrong frame of mind, then that's the manegement's fault. If people want to boo because they've spent hundreds of pounds to bring their family to a game, and they're sitting through a snooze-fest of unmotivated, distracted individuals, then that's their prerogative.
The topic of massive money is most definitely NOT off the table. For massive money, you should deliver massive value. It's a simple rule of economics (the 'it's worth what people are willing to pay' isn't relevant to player choice since we don't decide who we buy or who plays). So when they play, we get to show our discontent. Ultimately, it's down to the player to be responsible for themselves and listen to guidance and advice, if they ignore it, that's on them. If they are played when they aren't right, then that's on the manager and they should be the subject of criticism. Booing isn't going away. It's primal, it's honest, it's crowd mentality, it's theatre. And that what we're paying for.