As an" outsider", I can see the logic of "paying by weight" for Airport and Ground-handling charges.....It's self-evident that a 50 ton lump is going to cause more wear and tear than a 35-ton lump......it's not linear, of course.
The road-transport industry had l long fight with the Eurocrats because Continental lorries were allowed a higher axle-loading than UK ones.....hence a spate of bridge-works, roadwidening, bend-straightening and sub-base replacements. IIRC, a 10% extra axle-loading = 30% extra road-wear.
So, One can understand an "ON THE GROUND" weight-charging regime.
pax or cargo is not relevant, because the pax-charge is on a per-head basis.
Once off the ground, a big jet would appear to use exactly the same resources as a private IFR flight.
Logic dictates that an empty positioning flight should be cheaper than a "full" flight, all other details being the same.
Common-sense dictates, therefore , that the element of trust works BOTH WAYS....."euro" cannot expect the same revenue from a full aircraft , as an empty one. If the "certifying authority" is willing to issue a "weight-certificate" on an individual airframe/flight basis, that seems fair, reasonable and logical, given the Eurocrat's (allegedly) entrenched dogmatic and inflexible position on this..........no different to lorries going in/out of a facility via a weighbridge and levies being based on that factor.
but what would I know, I don't have my snout in a trough of gold.