Sorry -no sympathy from me for being too late.
The information about needing to be through security 35 mins before flight departure is shown clearly (in bold font) in the "check in options" of BA.com, as well as on the boarding pass that you printed out.
The reasson that all airlines have cut off points is so that everybody knows the score - what you seem to be suggesting is several different times, depending on circumstance...how about:
35 minutes before when its "busy" - who determins what "busy" is by the way?
30 minutes if its just a bit busy
25 minutes if its quiet
20 minutes if you havent got luggage and its busy
15 minutes if you havent got luggage and its not too busy
etc, etc
The point is that you should have read the requirements and made your flight booking/meeting times around those - especially as you were taking the Heathrow Express - so more potential for delays.
Take responsability for your own actions and stop blaming "the system" for your own late arrival
Not a banker by any chance are you?