You are, of course, entirely correct. Some castings and fittings are so poor as to be unusable and there can be no excuse for that. However, as far as kit producers are concerned there's a quality/cost equation. Can something of good quality be produced at reasonable cost? The answer is, as we know from these pages, that it's an equation which can be made to work, but the kits which are available and which are delivered with usable castings tend to be on the more expensive end of the market. Even then they may not be perfect as perfection arguably requires bespoke items often produced as "one offs" - the casting processes are inevitably a compromise to some extent but a 3D print can be accurate to the nth degree. However (as a generalisation) 3D prints are expensive and would add ££££s to the cost of a kit.
Having built a couple of kits by MOK I have to say that I was able to use all the castings although they all had to be fettled to some degree. But those kits are at the top end and can be compared with kits costing half the price but will be (again a sweeping generalisation) half the quality.
Basically you get what you pay for. If you are willing to shell out for bespoke castings most kit producers will sell you "etch only". The cost for the bespoke items may well make your eyes water.
) needed beefing up a bit. So I replaced it with some larger diameter rod. I also added a representation of some flange connectors by drilling out some crankpin nuts and slipping them into place.
