> except for maybe not being able to choose the output lane for inserters, but that limitation is as old as the game itself, and I don't know whether it's a misguided design decision or simply a limitation of their extremely optimized belt system.
I think I might have some good news for you, this was added this summer with the extension of the “flip” mechanic
sadly, that only applies if the belt is perpendicular to the inserter, not parallel (i.e. you can pick left-right, not near-far), so it's only half-great. it addresses the major inconsistency with non-trivial belt configurations breaking when flipped rather than rotated. the minor inconvenience of assembly lines requiring a small lane-switching segment on their output belts once one lane is full still remains.
Output lane switching is possible - some mods (e.g. [1]) add it, as well as even wilder options. Not offering it in the base game is a deliberate choice.
As far as belt lane management goes, another interesting option - which is also present in the engine, but not used by default! - is lane splitters [2].
I think I might have some good news for you, this was added this summer with the extension of the “flip” mechanic
https://www.factorio.com/blog/post/fff-442