Not rare at all i would not think, from MEL when the BA, SQ, and QF flights all used to leave within a few minutes of each other they used to shall we say have a race, one night i even asked the cabin crew to ask the pilot who was beside us... he replied that it was the BA plane we just overtook and we took off atleast 10 mintes after them
(i am thinking it was MEL-SIN .... but maybe i am thinking SIN-LHR)
I have seen it many times on some of these routes.
E