The issue is not that new properties exist.
Well ... for you, I guess. El_M seems to be disputing it. (I think?)
The issue is to label this phenomena a case of the sum being more than its parts. At least when we say the same thing about consciousness.
Which phenomena? "A case of the sum being more than its parts"? You mean "emergent"?
If your point is simply that we don't know for certain that consciousness is emergent in the strongest sense, then ... sure.
I'm saying that recombining oxygen and hydrogen certainly modifies the resulting compounding, giving it properties that are akin to those of hydrogen and oxygen, maybe shifted. Just like a fire and the sun have the property 'heat'. So does an icecube. Same property, just different along a gradient
Water is an example of the principle of one sort of emergence, in that you do get some qualities that neither hydrogen or oxygen have. Water expands when it freezes, as yet another example, despite not having an "ingredient" that does so.
The wiki article lists several types of emergence. Water having different qualities would belong to the most trivial sort. More of an example of the basic principle than anything else. Consciousness would be the most err, the most "substantive" type (picking the most ironic word), where the existence off the emergent "thing" might be immediately dependent on something non-material.
Not that matter isn't involved, but consciousness may be more like swarming behavior than friction. The latter has a host of physical processes that, working on a micro or quantum scale, give rise to macro-scale friction. Swarming behavior (itself a non-material thing, OTOH, is rooted in biology but is "made of" math.
If consciousness is like friction, then it's a matter of learning about what exactly all those little particles, waves, and wavicles in our heads are doing.
If consciousness is like swarming behavior, then we'll have to understand
more than the physics of our brains. (Or, really, perhaps less ... The math may be easier - less complicated and easier to perceive - and than the physics.)
Note that in either case, we could potentially make some rather good rules/predictions about consciousness despite not understanding everything down to the sub-atomic level. Just as we can with swarming, or to a lesser extent, friction.