When it comes to fits and faults, let's not generalise. Each ship is different, and some problems are harder to fix.
The root is a conflict of priorities
Builders wants something that is broadly accurate in basic form and fits well first and foremost - there's no point to have extra detail when to fix fitting issues one will have to destroy the detail in the process or have a crack of a grin on the hull.
Companies are designing kits to quick to market and look good in the box. After all the pitfalls will not be known until the model's bought and actually built, and most 'review sites' that companies supply kit to do in-box reviews which are half relevant.
Make large pieces fit together well is a lot harder to do than mold 4 side walls of a box each with engravings. I respect Tamiya not necessarily because their research (which can be crap for non-Jap subjects, but then there are very few), but because of quality. Things fit. Edges are sharp. Engineering is smart - there's thought behind the parts breakdown to make the modeler's life easier.
On the other hand, some companies currently aim at people who like things that look pretty in a box, but hardly build, or are not very particular about quality of their builds. This is a marketing philosophy I disagree with, because I see it as a cop-out.
It's hard if a modeler must resort to carve up the model because the basic shape is wrong.
It's hard to make sharp edges from soft angles (but easy to do the other way around, why I have no idea!)
It's hard to be presented with a bunch of detail that are overscale, which needs to be removed, then proper ones added - I'd rather it be molded plain to begin with.
Oh, and finally, Tamiya Scharnhorst molded the stern in a separate piece, and the reason I suspect is just to fit the hull into the then standard sized box.