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].
[1]: https://mods.factorio.com/mod/quick-adjustable-inserters