It puzzles me that Heathrow movement levels have never got back to pre 2001 levels even though, as you say, it is said to be full. The daily record hasn't been broken for ages, I think it is around 1370. This Friday there were only 1329 moves - and Friday is supposed to be one of the busiest days!
Also, there was a time when you almost never saw Regional Jets at LHR, which suggests pax loads are decreasing on some routes, presumably due to the low cost carriers taking business away.