It's true that it will take 3 minutes less to reach Heathrow T2,3 on Crossrail from Stratford than Southend Airport by train, but as been pointed out before, unless things change dramatically the train to departure gate will lose you a great deal more than 3 minutes at LHR.
Remember there will be no direct service from Stratford to Heathrow until December 2019. The central Liverpool St to Paddington section will open then linking east to west. So the SEN-MAN flights have a couple of years to prove their worth before the threat that LTNman talks about. Time enough to become established if the demand exists.
Last edited by DC3 Dave; 4th Nov 2017 at 12:28.