Could be an element of truth in that but I don't think they're the only or even the main factors.
For a start HK is a long long way beyond Beijing and you have already overflown almost all of China on the way there, so almost everything China from HK is doubling back on yourself. CX are also significantly more expensive than HU (with good reason).
I do think HU suffers some structural disadvantages in the MAN (or UK in general) to China market.
1) Brits love their frequent flyer programs and particularly the main three global ones so if you're flying to PEK from MAN you can fly through AMS, FRA or HEL and get a stack of points for your trouble - or with HU where you don't.
2) There is a brand awareness issue - even after 3 years - before the last trip someone asked me who I was flying with followed by the almost inevitable 'never heard of them' response. Another popular retort is 'sounds a bit dodgy to me'. Brand awareness is not an issue on the Chinese side though.
3) Decent connections at the PEK end are limited and naturally limited at the MAN end despite a few UK and Ireland ones from other airlines that tend to get called out for a passport swipe prior to boarding. There is also the possibility of having to switch terminals to make a connection as well which in both airports is a nightmare. This might imply an over-reliance on point to point MAN-PEK.
There's no doubt either that at 4pw it is not ideal from a business perspective (it always works out that either the inbound or outbound leg of any trip won't work). I've had agents who when confronted with one leg being non-op revert naturally to the 'safe' options through a hub. It is only because of my strong knowledge of who flies where and when that I can correct them.
Given all the above disadvantages it is perhaps a testament to the strength of MAN and the route itself that it's just completed three years of ops.