Well you can always ask the developer to split the prestige in the End Game or even the main game
So you get PP points for how much your asso has hauled and PP points on how much you hauled and then you add them up. So if your asso is 1st you get e.g. 1.000 PP and because you were 12th of all people in the city (incl other asso) you get another 250 while the 1st guy (irrespective asso) will get eg 1000 PP.
But do note that my belief is, this will make it even more difficult to stop outsiders to start hauling crazily - you will probalby cause more problems than you fix. Also the developers might not like it because this all comes from players who are not spending crazy money, and they want the crazy money people to create the wealth.
Food for thought as I believe you will never find a system that makes all happy, maybe not fix sth that is not broken? Probably changing anything in the EG will cause more discussions than solutions.
By the way, I like the current system, as long as people respect the city. Personally I setup a network around a city that doesn't go to EG so I use my fast trains to haul some staff to the other megacities (like 10-15 tons etc) and this way I can use those unneeded industries and make some small prestige with the current system that will increase my gold earnings without affecting the city... so I am good with it