Skipness - The three carriers you cite have a vested interest in filling capacity dumped at LHR in order to support the frequency they require to compete effectively at the front end from London. They have a surplus of economy seats to fill in particular, and it is quite common to see a MAN-LHR-USA Y-fare cheaper by GBP200+ return than the equivalent MAN-USA. A significant premium is applied to the non-stop MAN departure to encourage flows by price-sensitive leisure customers to those empty seats ex-LHR. A family of four can often save GBP1000+ by transferring at LHR using the same airline which offers Transatlantic non-stop from MAN.
MAN also has to contend with 'sweetheart deals' whereby specialist tour operators and cruise companies receive block discounts to fill capacity on LHR flights rather than the MAN alternatives. And then there is the issue of corporate travel policies and loyalty schemes which also divert passenger flows onto less logical routings. MAG needs to work on these continuing challenges.
As you know, Delta is now working in close partnership with Virgin Atlantic in which it owns a significant stake. It makes good sense from a business point-of-view to use Virgin metal on the MAN-ATL route. The A333 is a capacity upgrade on a route which can be leisure-heavy with passengers connecting through to Florida in particular.
In terms of allocation of the B788, it is normal for new state-of-the-art equipment to be allocated to the high visibility glamour routes first. At MAN, we are accustomed to having to wait patiently in line on that score.
One interesting development to watch is the introduction of Thomas Cook A332 schedules to JFK and MIA this Summer, traditionally routes we associate with dominance by the US majors. If this initiative proves successful, the three US majors will be less able to dictate traffic flows on routes such as New York (JFK/EWR) by strangling availability of capacity.
It is not long ago that MAN filled a daily B763 and a daily [BMI] A332 to ORD. Those passengers have not evaporated; they have just been forced to re-route due to capacity decisions made by AAL which has alot of empty seats to fill ex-LHR in partnership with BAW.
Just a friendly reminder, Skipness. You keep coming on here to ask us questions (to which I suspect you well know the answers already). We respectfully rise to the challenge. But afew days ago I asked you a very specific question in return. I'm still looking forward to the courtesy of your reasoned reply :-)
PS. Just a footnote to compliment the outstanding series of postings by 'philbky' over recent days.