I see a lot of bikes that the pulley cages don't maintain "perfect" alignment with the cassette (as in the cage/pulleys being parallel to the cog's plane through the complete rotation of the cage pivot) that work well enough to not be an issue for adjustment/indexing or actual off stand riding.

I think that there are a few contributors to this. First is the cage pivot bolt connection to the cage not being really square (cheap ders often have a peened/riveted connection). Next up is the der mounting bolt (the "B" pivot). Between poor threading (how many ders do a wobble while threading into the hanger) and/or the stack of spacers and "e" clip the mating surfaces are not as consistent at locating the der upper knuckle square. Add in the slop between the many parts, due to manufacturing tolerances and wear, and that the chain is often placing lateral force on the cage with cog/rings that are not of the same chainline and it's no surprise that the cage will be off parallel.

All this is independent of hanger alignment. When I do hanger alignments I use the actual der (and its cage) as the indicator to best alignment. Yes, this is not what instruction manuals and ideal worlds think is The Way. I do this because the der on the bike is in the real world. I place the chain on the middle rear cog and the middle front ring (or both of a double, one at a time) and make sure in this "average" der cage placement (both laterally and rotationally) is as well aligned with the cogs as possible. Yes, this means taking more time then just assuming the tool's alignment will always be the same as the actual der.

So my standard is based on the parts in use and their condition. Change the hanger or the der and I will suggest revisiting all this to confirm. Of course better parts tend to have less manufactured inaccuracies and might wear better. Back pedal too aggressively when the der isn't lined up with the cog and this can change as the bending forces might be too much for the der to handle (having watched a demanding customer do exactly this on their pick up test ride...).

Sorry if it was my mention of seeking help that wasn't helpful. Andy