I haven't seen recent data but that certainly used to be the case. However, the crucial difference is that neither CDG nor (to a lesser extent) FRA have the same barriers to entry as LHR. LHR is operating at around 98% of the maximum allowable number of movements.
Where it is possible for new entrants to come in, monopoly concerns are much abated. That's also why there is little evidence of high slot values at either CDG or FRA.
In any event, just because someone else might be getting away with it doesn't make it any more acceptable!