OK, but only a minority of flights actually depart from T5C, there are plenty from the main building which do not even involve the silly train
But another problem is some of those flights, some longhaul, some shorthaul which seemingly depart the "main building" in reality depart from a remote stand which can on occasions could involve a bus ride out to the stands beyond T5C....seeing as the last bus for these usually roll out of T5A around 20 minutes before STD there's still no scope for "runners".
Having said that I'm not a fan of the -35 minute rule either, but as SKipness 1E rightly said " BA's on time performance was in the toilet at LHR".