18+ years to LH command? That is truly horrible
The time to a LH widebody command in BA has been well into double figures couple of decades at least, but there used to be a fair chance of picking up a shorthaul command earlier in your career as some the shorthaul Captains moved to longhaul to replace the age 55 retirees. The issue now may be that with minimal retirements from any fleets the time for a shorthaul command will possibly also go out into double figures.
FWIW I was 16+ years in the RHS of a LH type before command, and given BA's route network I certainly didn't find it "horrible", there were worse places to be - but it's whatever floats your boat I guess.....