Thanks for sharing your thoughts... as for what you say, I suppose the value of subjects like this and the precision in terminology depends on what you elect to do with it all.
Setting aside the technical specs of khandha for a moment, I find the term upādāna, defined as "appropriation" (as opposed to "clinging") to be immensely valuable in practical terms.
For a while to me, the term upādāna seemed pretty much undifferentiated from tanha (craving) - maybe an attenuated or stronger version perhaps? Perhaps it's clinging to what you craved? etc. That perspective was not very useful.
Regarding it as "appropriation" however, I came to see the true meaning behind it - i.e. the etymological "taking up". To build samsaric experience in one of the planes of existence (bhava), we need to take up things as "self" or "mine". Seeing what we take up (including the paticcasamuppada dependencies behind it), and understanding more about the nature of what is taken up, and what it actually is, helps guide on just what should be put down and let go of, and also importantly why
(i.e. if you don't see
how "letting go" leads to benefit, there will be increased resistance - it's a hard enough habit to break as it is).
It's often said that the instruction of "let go" is an over-simplification, and in many ways it is... "let go of what?", "how?", "do I have to give up all my possessions?", "do I have to let go of my desire to follow the path?" and other circuitous nonsense. On the other hand, I think upādānakkhandha explains precisely what it is we're meant to let go of and how. Without that, it would be all too easy to fall into the trap many modern Zen-noobs fall into... such that the pinnacle of Buddhism is understood as "blanking out", that thinking is bad, and other such things that find no support in the Buddha's doctrine etc.
Consider this standard satipatthana refrain, in light of the above...
His mindfulness that 'There is [x]' is maintained to the extent of knowledge & remembrance. And he remains independent, unsustained by not appropriating anything in the world. This is how a monk remains focused on [x] in & of itself.
The much lauded observation of "rising" and "falling" that precedes this refrain helps me become disenchanted with that which could be appropriated and gives rise to the observation of "rising-falling-dhammas" (as per that cool topic you started recently) and that in turn serves as an entry point for me into this specified mode of awareness, rather than the observation of the characteristics of arising and falling serving as a full and complete approach in itself. I think this "refrain", despite its regular appearance in the Satipatthana Sutta, tends to get blotted over and ignored in contemporary discourse on vipassana as if it were not relevant, or just bonus waffle.
(It's probably worth at this point highlighting that this approach differs from the "cut it into more pieces" approach, as it is actually disenchantment with the very act of cutting and with what was formerly cut. As such, it simplifies things back up to the mere "there is [x]". This probably deserves a topic in itself but I don't feel like creating one just at the moment. Maybe soon.).
That is how I understand and apply the sutta in this regard.
Alternatively, it could be used as a "recipe for overcomplication and distraction"... it all depends on what you do with it. For me it's a means of simplification and non-diffusion.
Breathe deep and let go of things.