Yes and there's been a LOT of feedback about colonization ignoring all other professions and focusing on JUST hauling. However that fell on deaf ears so the last hope was that the PC MKII would alleviate the pain of endless of hours of A>B>A hauling.
you are giving the answer to yourself (not that it was already given by many players in the forum): The cargo size of the PC does not play a role - it is the game play:
The limitation of the PC's cargo size makes sense, albeit it could be also 1500 or 1600 but anything larger breaks the coherence of the game. No matter how ED is classified as being an MMO, a sim, a space opera - it has to be grounded in its own (pre-defined) logic and cohesion or it becomes random and frustrating as we can all see with certain movie franchises (hi, 'Terminator Dark Fate", hello 'Romulus'). I haven't heard of many retcons which were well-received by fans.
Going the route of fulfilling the wish of an uber-ship leads to a small size ship which has 10 huge hardpoints, 5000 t cargo, massive powerplants and a jump capability of 10000ly etc. What would everybody fly? Yes, exactly that unicorn and nothing else. Would that be a better game play? I leave that to you to judge.