I transited in LHR 5 twice very recently. So did my family on different days.
The security clearing does indeed take long and all agents look at you as a potential terrorist. But the lines are well organized and it never took any of us more than 20 minutes (with a norm of 10-15 min).
That is too long, unpleasant, and a sufficient reason to try to avoid LHR. But nothing like what CDG immigration has become.