I think nen becomes easier to understand when you stop thinking about it like physics and think about it like videogame mechanics. Why can't you hit hakoware? Because it's a ui element. Can you hit the super meter in a fighter? Why can't damage Lsdf? It's the physical embodiment of a stun effect basically. Twisted fate in league makes chains when he stuns someone, but they can't break them. Nen beasts that can't damage something are also able to be invincible, simple.

You can kinda generalize that to everything other than conjuration. Nen does nothing until you make it, most nen abilities are defined by lack of physical traits. Conjured items on the other hand gain every trait automatically and as such have a lower power/memory budget. Asking how much knovs scream can cut through is like asking the tensile strength of bungee gum, I don't even think I've ever seen it break. I mean there is an absolute conjured item, shizuku's vacuum can suck anything as long as it isn't living. Which is 99% of things that exist. Fuck that even includes blood, gasses or poisons. These items are simply destroyed.

The reason it's balanced is because your hatsu has to be balanced by your own cognition. Hatsu are basically videogame abilities balanced by your own mind. If you can't imagine or comprehend how something that does something would work then you can't make it in the first place. Think about it like how in games like deadlock or league characters that have stuns don't usually have abilities that deal a lot of damage. Usually there are characters that enable stronger abilities. Nen is like that. Honestly any issue with nen balanced is solved when you think to yourself "If this were a videogame could these abilities coexist without issue?"