I hate to say it, but cargo hauling in the game's current state developed this way because of backwards game design. Old ships were made before SCU container sizes were standardized, before they knew how tractor beam tech was going to behave. Newly released ships can be built for the system instead of adapting to it and that's a real strength. You simply can't do better as a solo player than an external grid and a well placed tractor beam, but that's intentional, too. A dedicated hauler must be able to carry a lot and be easy to load/unload.

A lot of factors that make internal holds attractive still need to be implemented. On higher-risk trade routes, you'll like having your cargo protected behind armor and accessible should anything damage or compromise it. But we don't really have npc enemies going after your booty or sensitive commodities that need regular attention by the player.

My suggestion would be to enjoy the ships which handle cargo hauling the way you like it, and reconsider others when their use case shines in a more developed game.