I agree that Blavatsky might have been too extreme to use as the basis for an IP about DIY magic, but I don’t think “consensus reality” is all that great either. It plays right into science denial and postmodernist critical theory. E.g. flat earth belief, anti-vaccine sentiment, “woman is a social construct.” I don’t want to see those promoted as truth even in a fictional context.
But I digress
The digression is more interesting than the actual topic though and is at least game related.
The thing to remember about “consensual reality” is it’s pretty much jargon in the same way that “disk drive” is in this era of solid-state flash drives... or the fact that the save icon looks like an old 3.5” floppy disk; it’s a term used even though it’s not actually all that accurate because it’s familiar and still somewhat covers the part related to magic.
Because, since pretty much late 2e and continuing through Revised and V20, the ACTUAL cosmology would be better described as an objective universe with will-based reality warping as an overlay.
That’s because late 2e on introduced the idea of “cosmological constants”; gravity, linear time, a round planet that orbits the sun, basic physics and chemistry; all of that stuff (among others) in Ascension has been established to exist independently of any will.
They also clarified “effect-based determinism.” i.e. the result of your magic is limited by the spheres used to produce it... you can’t use Correspondence to coincidentally get quickly across town by having a Taxi show up (that would be results-based determism... Correspondence allows quick travel from place to place so a coincidental use is that a Taxi just happens to be there and gets all green lights the whole way).
Rather, to just happen to have a Taxi waiting on the corner you’d need matter (to create a taxi), life and mind (to create a meat puppet taxi driver), prime (to create those from nothing), forces (to control the traffic lights) and correspondance (to affect anything beyond your line of sight) and a generous helping of knowledge in engineering (for the taxi) and biology (for the meat puppet driver).
In other words, Correspondence alone doesn’t cause reality to subjectively produce a taxi and driver. You have to deliberately warp reality using specific knowledge of many spheres of magic coupled with principles of physics, chemistry and biology.
Another example is that if you want to survive being shot by the bullet coincidentally hitting a whiskey flask in your pocket, then you better either already have a whiskey flask in your pocket (and either entropy or forces to guide the bullet to the flask) OR have matter magic to create a whiskey flask in your pocket.
M20 also clarified “hypothetical average observer” for coincidental/vulgar magic which further defines a less subjective and more objective reality. If you walk into a dark alley, no average person watching would think anything of it. Even if they were following you and couldn’t find you when they entered the alley they wouldn’t think “magic” they’d think you slipped out via a route you didn’t see.
Similarly, if you walked out of a dark alley on the other side of town, no one is going to think “magic” unless they knew for a fact you were 5 miles away 10 seconds ago (though if they did know that’s now vulgar with a witness).
Basically, all of these combined establish a non-consensual reality that mages are able to warp using their belief (bolstered by the tools and practices they believe work) to the specific limits of their avatar and will/arete... and which gets pushback from both the degree it violates objective laws (vulgar without witnesses) and even more severely from the unbelief of Sleeper (vulgar with witnesses).
Reality warpers with security blankets (their paradigm, practices and props) is really the only sort of system that can allow “everyone’s magical practices work” in any sort of coherent fashion. It’s also the version that best interacts with the broader World of Darkness and it’s need for certain objective truths for their settings to function.
The alternative is basically the largely rejected “one true way” approach that Awakening used.
So if it’s majority objective, why do they call it “consensus reality”? Because it’s an easy shorthand for explaining the fundamentals of the “reality warpers” abilities and limitations, but it’s about as accurate as claiming E=mc^2 is the whole of mass/energy equations.