You have to remember that not many people in the world want to travel to FRA or MUC. LH have these set up as hub operations with so much connecting traffic. Those who are going may have a decent amount of business purpose travel. I woudl guess about 70-80% connex?
On the other hand, LON is a destination that people want to go to. I do not think of BA at LHR as a hub operator - the slots do not enable them to work the bank structure that true hub operators have. Instead they have a lot of flights going to London, with the major benefit of being able to connect these pax on for the additional revenue. I would say this is about 30% on average?
If BA became the LH type of operation then they could do in MAN what LH do in MUC. However keep in mind that the business demand for MAN is never going to be enough for a full network operation.
Also, if we compare the UK to Germany, BA has had a secondary carrier to contend with on both markets - bmi on shorthaul and Virgin on longhaul (now bmi also on longhaul) - LH have had the benefit of not having such major carriers restricting growth - thus being able to grow to wherever they want - and get all pax.
Also on low cost, the UK has had fierce competition from the likes of easyjet and Ryanair also snapping at their heals - whilst this doesn't impact on longhaul it does on shorthaul which doesn't help a carrier when trying to grow - hence I think their decision to not focus anything elsewhere.
And you should also compare the amount of other longhaul flights to MAN vs MUC - I don't know much about MUC, but if you consider MAN has ORD x2, JFK, EWR x2, ATL, MIA, BOS, PHL, IAD, MCO, LAS, YYZ, YVR etc it doesn't mean you can jump in and dominate!!
At the end of the day (and being ready for abuse) I think BA have done the right thing in staying away from MAN and focusing their longhaul efforts on LHR where the true demand is.
I think people forget how much more competitive the UK has been for many years versus the continent so don't think any useful comparisons exist.