I'd suggest anyone to try and get the best possible contract as long as they're part of the same capitalist system, no matter if they perform or don't. We don't exactly live in a meritocratic version of it and I don't see why he should be ruled out of Glazer (or any entrepeneur, basically) money. Sure, I get it should not lead to disturbances in hierarchy in case that's a main asset of your club, but I'd love it if my agent got me a better contract. I might need to change jobs and I sure hope that the money at the least doesn't get worse, especially since most of the jobs currently available to me aren't my passions. I hope for Mainoo that football comes closer to that feeling for him, but since he works for a very corporate club in a very commercial entertainment system, I don't see why it's bad he asks whatever he's asking.
Whether he should get it from the club and if it's good for their future is another thing, but that's why there's discussions to reach agreements. There's a reason the number one tip when getting into salary discussions is to ask for more than you're expecting to get. Who knows, maybe you're lucky. In the end, outside of having lost their private lives and since the internet having to deal with public backlashes (even) more directly, there's no ethical reason why a good football player deserves more money than a bad one. Or why someone good at trading deserves more money than someone who sits in their room writing poetry.
Football players get a lot of money because this is an entertainment business. But Harvey Weinstein isn't the reason I watched Inglorious Bastards. But I'm pretty sure at the time there's a good one he was the richest name attached to the project. Just like I'd rather watch Mainoo kick a ball than this old guy who buys shares to increase his assets and asks his communications department to write a speech that makes it sounds like he's doing it all out of love for the club.
Again, for the future United has to make a balance and follow this up with well thought out decisions, amongst which how much they want to increase the job offer's benefits. But I'll never blame Mainoo and others for aiming high.
Personally I don't care (enough) about money (on its own) to be able to hard ball in talks like this, plus I would like to have some certainty about my future if possible, so I'd probably act differently if I got an amount that's already insane (I already make more than I expected two years ago, and I don't even want to calculate what the difference is between mine and Mainoo's current income
Besides, what if he invests this money in more ethical fields than these owners and investors would? Why not support such a move? Am I not capitalist enough to support the big guys as much as I should? I really don't get it.
I have no idea what he'll do with his money, but I know a bit more of what people like Musk do, and then I'd rather take the gamble with supporting this teen, that I don't know besides highlights, a few games and occasionally using him in my eFootball team, honestly.