I agree with op that it would be nice for Valheim's build system to work more like real static structures engineering, but it isn't true that you can't build with it. You just have to accept the fantasy physics of Valheim.

Presently the only thing that matters is how many pieces you are from the ground, as indicated by the color system. There is, I think, more penalty for horizontal distance from a grounded piece, but I haven't observed that carefully, I just watch the colors.

If a brace is attached to, say, a green vertical, it should transfer green support to the piece it holds, or so I assume. That is surely in the works if not currently implemented.

And I agree generally that the build system needs to get better, even though you can build some amazing stuff within the current limitations.

On the other other hand (if I haven't lost count) overcoming limitations draws out creativity. It's a thing. Poet's write to some strict form like a sonnet in order to force themselves to cudgel their brains.

I think Valheim+ lets you rotate pieces on two axis? Might be worth a look.