So while the SSSS when boarding at LHR may seem a little extreme to you, I think that if there's anywhere I'd want it to be used, it's on flights from the UK.
Which makes it so ironic that on balance, LHR is perhaps the easiest airport to clear flights to the US from compared to most European airports. Depart from Germany or AMS for example and you will go through the obligatory "interview" of why you were in the country before check-in, then pass general security, and then pass another layer of additional security at the gate [which at AMS includes yet another "interview"]. At LHR, you check-in quite normally, clear general security and then board without any additional screening unless you have been flagged somewhere (which I have never endured despite dozens upon dozens of LHR departures to the US).
In fact, what the OP describes is simply SOP at most European airports for US departures. Only at LHR is this considered being 'singled out' for extra treatment.