I'm not really of the mind to break down the game of younger players as they should be allowed room for growth and mistakes in and of themselves should be expected from them. What you can do, however, is look at the base level, the tools they're working with and the potential you think you see in them by extrapolating upon what you see.
I watched the vid you put up and it's problematic because it's underwhelming. Great for Serie A, but not much in there I would expect to translate to the PL. A lot more space against players who aren't athletic and the technique on display is, as you say, decent, which isn't a good sign given he's going up levels coming to this league and will face opponents for which his threat isn't so much of a threat.
Contrast any vid of him you can find (I'm pretty sure) with something like this, from an even younger player:
And there'll be a sizeable contrast. This is the kind of player you want to endure the growing pains and mistakes of, and most likely very little of the time it'll be his technical level and competency under the microscope. We paid a lot of money for Dorgu and honestly you expect a higher level of technical ability for the outlay - a Manchester United player, or so the saying used to go. Now Quenda may be called an outlier and he cost Chelsea a lot more to acquire, but should the contrast be so extreme? Is the fee paid the going rate for a Dorgu with the technique he has? I don't think it is.
I think the question you should ask when it comes to the likes of Brighton and a player like Dorgu is whether he'd register as a desirable buy according to their data models, and then, how much they'd pay for him. I don't know what we were looking at when scouting him or what we saw in him to spend that kind of money, but I highly doubt the kind of teams you're referring to in the PL would have done the same. Your point about them developing unpolished gems is a valid one. I don't think this is the kind of gem they'd actively seek in the first place.
Don't want this post misconstrued because I'm replying directly to your post so it has to be objective and not filled with leaps or faith and hope. I didn't know anything about the player before we were linked and since he was, the deeper dive has been underwhelming to me, especially for what we paid. That's not a punt amount.
I sincerely wish him the best and it would be fantastic if he can kick on, but him being such a key component in our attack is far from ideal for him and us.