Not that simple. CX are able to efficiently provide for a more evenly distributed schedule, whereas BA needed to follow a similar routine for aircraft utilisation, (BA planes are already on the ground for several hours as it is) with evidence that a morning LHR departure arriving dawn HKG, returning morning from HKG into LHR afternoon would not be popular - it is either that or a 3rd almost identically timed flight which yields probably cant support. I think the 3rd also was helped when there was more of a joint business with Qantas.

The fact is BAs schedule only really works thanks to the very early landing pre-curfew slots it has, otherwise you have to hang around to past 1am to arrive for a post curfew slot. Which again isn't ideal.

So CX does give you more mix and match scheduling if you prefer a day flight to LHR - but other than that I'd choose BA.