I'm not forgetting about fuel, and gave the most optimistic numbers I could. Weight for premium passengers (eg bigger more complex seats, more floor space, bigger toilets, more galley space, equipment and food/drink) should be allocated to them, not shared evenly. I also don't think it is fair to allocate items like duty free carts, or what belly cargo is using. At the end of the day if you do a more realistic and fair allocation (~half the plane is not used by economy passengers), especially what people have control over (I didn't ask for duty free, dead heading crew, alcohol etc) then the weight differences between economy passengers still are not significant compared to the big picture.
Your example is not entirely appropriate because first you're comparing 2 classes of paying customers: the ones that paid a lot, and the ones that paid a little. Then you compare a service that's provided for all passengers equally, like the duty free.
My point was being overweight is free, being "overheight" or an invalid will cost you every time. I have to pay a lot more to get the same level of (dis)comfort that everyone else gets for free.
It's the kind of discrimination that people just let slide but it's discrimination nonetheless.
i think we are talking past each other - my point is that passenger wight vs total weight is not a very relevant metric - you need to think about in the context of payload [https://commons.wikimedia.org/wiki/File:Takeoff_weight_diagr...] which can be as little as ~10% of MTOW
350k kg max take off weight -170k Kg empty weight -145k kg max fuel = 35k kg usable weight @ max fuel
35k kg / 350 pax = 100kg/pax which means passenger weight is far from trivial