2 hours does seem very excessive. Most LGW-LHR T3 coaches are around 1 1/2 hours during the mid morning period likely when you will be travelling (assuming you'll want to arrive at T3 for around 1pm)

As to the BA 271flight the most likely reason is the plane due to operate the LAS flight is delayed on it's in bound or there are late swaps because of earlier flights going tech. Nothing really to do with ATC or inefficient BA staff