MAN is also my local airport.
Short haul Avios redemptions are a bit of a nonsense. However it is possible to get the train to LHR or LGW reasonably cheaply.
But rather than throw my hands up in horror, I have been doubling down on my Avios because there are lots of other options.
Cathay to HKG and Qatar to DOH and Finnair to HEL all give good opportunities. Especially DOH where the Qatar redemptions to places like BKK are cheaper than going on BA.
For ultra long haul you are going to be changing somewhere from MAN whatever airline you fly. So it may as well be LHR.
The redemption treadmill at other alliances is a lot harder to deal with for me as I am no longer a regular business flyer, so can't easily get status and run the risk of miles expiring.
Believe me I have looked!
SkyTeam and Star Alliance really require you to have a European address to get the decent credit card deals. The UK is shut out.
There are Virgin options, but they aren't as lucrative as the BA ones IMO.