I think a lot in your post reflects the thinking of top English clubs. These kids are never ready it seems. There's too much pressure at this level to produce results and buy the finished product.
As the poster a few posts above stated, lesser leagues afford kids more time to develop in the first team at earlier stages of their careers. Clubs like Ajax and Dortmund have made this part of their business model, Ajax more so since they focus on developing players in-house.
I'm certain Habbibal would be getting more opportunities outside England in my humble opinion. By the way he played in the Arab cup as well. I also don't know how you can conclude that his temperament is less suitable for first team football than Bellingham and Camavinga. What do you base that on?
Top English clubs don't have the patience to throw teenagers in the deep end, unless they are surrounded by seasoned pros within a system that they know what they exactly have to do....especially for someone who would play in the center of the park. It's the most demanding area of the pitch, central midfield is. When you're in a top team like City, Liverpool, or like what United used to be, you can afford to integrate a few young players because you know exactly what you're getting from the other 9 or 10 starters and top substitutes. With Hannibal, it's going to be anyone's guess half to half, let alone match to match.
The lesser leagues just don't have the pressure nor scrutiny that the PL does at the top end. And coupled with a club like Manchester United that gets attention for anything good, bad, or made up, it's a highly volatile situation. I think the fact that Hannibal isn't English is a blessing for him...it's less scrutiny and he wasn't a massive transfer.
He would be getting more opportunities even at a lower league or lower English level. 100%.
Hannibal hasn't been exposed to the experiences as a teenager in men's football week in, week out like Bellingham or Camavinga. Bellingham as a 16 year old in England, then plying his trade in Germany. Totally away from his normal surroundings. Similar to Camavinga. First team club football in France and then moving to Spain. Yes, Hannibal moved away to England, but then having to play week in, week out on top of your living environment is a lot.
The Arab Cup is level(s) well below ACON and if it wasn't, then he'd presumably would have played. But he didn't because the stakes and pressure was much greater at ACON.