I agree with everything you said, but I'd like to defend the main bus as a learning phase.
The main bus is for production capacity discovery. New players have to discover the production tree somehow and browsing recipe cards with a calculator before starting is not the way, it has to be hands-on and interactive. Dividing up your factory into (arbitrarily defined) intermediates production and final product production is helpful to cut through the complexity. Of course, intermediate production will be severely underbuilt and logistics capacity will never keep up with consumption of all of the final product builds, but it will be enough to run a couple builds at once and test new ones.
Once new players have a grasp of the scope of the production tree, with tangible examples of sub-factories, then they can begin to consider end-to-end production capacity.
The main bus is for production capacity discovery. New players have to discover the production tree somehow and browsing recipe cards with a calculator before starting is not the way, it has to be hands-on and interactive. Dividing up your factory into (arbitrarily defined) intermediates production and final product production is helpful to cut through the complexity. Of course, intermediate production will be severely underbuilt and logistics capacity will never keep up with consumption of all of the final product builds, but it will be enough to run a couple builds at once and test new ones.
Once new players have a grasp of the scope of the production tree, with tangible examples of sub-factories, then they can begin to consider end-to-end production capacity.