I’m another old and retired one but I agree with almost all the above.
If the eventual intent is BA Longhaul I certainly don’t see the logic of delaying getting a foot on the BA MSL by going off to Virgin for a while just to get a few heavy hours in with a plan of hopefully, eventually, slotting into the bottom of the BA seniority list, hopefully, eventually, perhaps as a LH DEP in a year or two’s time,,,
Getting the earliest Date of Joining you can is unbelievably important at BA, most especially during periods of high recruitment.