I agree that this is a methodologic assumption. The "lower" categories are not any "less real" than the "higher ones" in a subjective sense. But the more general category is more objective. The idea being that, no matter how you look at a rock, you can always see it as a collection of forces or particles. It is more general.
I also think the view that the rock is more real than the particles that make up the rock is an epistemological dead end. The entirety of scientific and technological progress is primarily driven by figuring out what stuff is "actually" made out of.
Imagine two people sitting on a hill top. They both witness lightning strike a far-off tree. The first person says, "That lightning is real for me. The experience of lightning is more real than anything else I could see. I am content." The other person says, "I want to know what that lightning actually is. What is is made of?"
The first person is at an epistemological dead-end. He can known nothing more about lightning.
The second person will go on to discover electricity, electro-magnetism, light-bulbs, radios, computers, the internet, Wifi, satellite GPS, and much more. All because they sought to better understand lightning in a more fundamental sense rather than seeing it simply as it is in a subjective way.
So I suppose neither view is "correct" per se, but one view has lead to greater understanding and technological progress whereas the other has not.
In what way does one lead to anything more than the other? Both are merely building abstractions. The one creates principles and systems which he attempts to apply; the other is substituting his own understanding of, or memory, or subjective experience, for the thing itself. The latter isn't experiencing anything except the arrival of a modulated nerve impulse, which in reductionist terms is nothing but sodium and potassium exchange over a membrane. Either way, we are treating 'reality' in abstraction. You cannot say one leads to greater understanding, as you are presupposing valence of what 'understanding' entails. This is the difference of the Taoist Sage and the Confucian, the Platonist vs the Aristotelian. We are debating the merits, but on what scale? Our Empiricism assumes intersubjectivity, which is highly problematic from a strict observational standard, so actually there isn't as big a difference as we think. Regardless we are looking at complex phantasms loosely connected to what they are meant to signify, and assumed solid.
Besides, we have no way of knowing whether electromagnetism et al. is any closer to anything. Remember, we know all our Science is probably wrong. Quantum Theory and Relativity Theory are a bit at odds, so we look for a Grand Unified one. This means that what we think we know we know to be deficient of the actual presumed end-point. It is all an abstraction after all, theoretical circles in the sand, unless you adopt some a priori Idealist notion. It isn't a mutually exclusive proposition therefore between your two friends on a hill.
We know science is useful, but little more than that. Much modern science is Empiric, so Empiric values predicting Empric results are still hedged on the presumed validity of Empiricism, even when we have 'predictive value'. Petitio principii, in other words. It means little, as old-fashioned systems like Galenic Physiology made positive predictions that were confirmed, but today we think the system wrong in entirety (for instance in Haemosiderosis, where the Galenists predicted bleeding would help and it does or how shockingly well it predicts Arterial Wave form). Or Roman Aquaducts built on incorrect ideas of pressure and flow, have worked for millenia regardless. Our Science too will pass away, and future generations will laugh at the silly things we thought, and they will likely be unable to show their ideas more fundamentally having 'greater understanding' than ours. For things often make long winding paths to return to favour or depart. Atomism was rejected as idiotic by Aristotle, the foundation of the tradition leading to Science today, only to return. The same with solid-state universes from the ancients to our day, multiple times. Or Aristotle's four causes, which we merely differentiated by field. Or Scholastics debating potentialities and modern quantum states. Or ether as unitary element, etc.
So neither can show 'greater understanding' nor can we assume technological progress. Progress implies a goal moving towards, but if that goal is itself a debatable abstract value... Lord Kelvin said heavier than air flight impossible, being a great Scientist with all the latest in scientific materials and meters at his disposal. Those with far less, much less technological resources, made him look a fool.
We are assuming the paradigm you prefer here, that asking how something comes to be, by reducing it, you understand it better. Perhaps the whole is more than the sum of parts. Losing the forest for the trees. After all, reducing man to his physiological homeostatic mechanisms and nerve depolarisations, you gain little real understanding of the creature in front of you. You gain insight into an abstract homunculus you made, a reduction to broad similarities or bell-curve generalities, which may or may not correspond. How can we even tell the difference between the abstract and the original it was abstracted from? We are creating a meta-narrative and presupposing it to be veridical. We humans are quite sloppy.
For you, what is the alternative to monism?
Dualism. I think there is something called 'I' and things beyond that. Often these may be intermingled to whatever extent, for I certainly agree a large part of my conception of myself has a physical component, but then I don't know where my concept of my own personhood begins or ends, nor if my conception is fundamentally valid. However, it clearly must end somewhere, or all bets for rationality and such are anyway off. So either it does or it doesn't matter.
Is not mind (or Mind) also just another category? Is not God just another category invented by us?
Seems like turtles all the way down to me.
Nope. The Tao that can be named is not the Tao. Read my first posts again. For us to be able to characterise at all, we are looking at potential metaphysical necessities here.