Have no doubt MAN will get a direct China link
I have no doubt either, particularly Hong Kong, as there is more than enough demand and I don't know about other airlines, but there are a significant and growing number of premium cabin fares routing MAN-LHR-HKG vv on BA, which suggests yield is there too.
MAN may have greater demand but there is also a lot more competition
Success breeds success. There may be more competition but that also means its much easier to get market data for a direct flight. If there are X number of people travelling on a premium ticket on MAN-XXX-China routing, then it may persuade another airline to want a piece of that pie. Sometimes that has been a detriment to MAN (Madrid is the prime example), but there have been times it has been a help too (Qatar and Etihad were initially born off data from Emirates and such, also Charlotte is helped by data of transfers via PHL that could be expanded via another hub.
Therefore, competition can be seen as a help just as much, if not more, than a hindrance.