I have the same challenge flying to MAN and usually end up taking the train from LHR. My approach is to take a direct TATL flight from the West Coast, get as close as possible to where I need to be, then take ground transit (appreciate that Scotland takes at least twice as long).

It's definitely nice to be done with traveling when you land but I find connecting further east just means more time on a plane/in the airport.

LGW might be tricky due to being mostly leisure flights. Virgin (and I think BA) used to fly LAS-LGW which is an easy connection from LAX. Might all be LHR now though.

If you want to go back to Virgin/Delta/AF/KLM could look at LAS to other places in UK. Virgin used to fly LAS-MAN and LAX-MAN should resume early next year which would get you a lot closer than LHR. Delta/KLM via AMS as well but I find it a pain for connections, perhaps Delta/AF via CDG?

Otherwise, OneWorld could look at Aer Lingus via DUB.