Well its a lot more predictable than chaotic, at least in the sense you combine a bunch of lean, analytical sounding components together if there was chaos then it would at least every once in a while sound pretty good. Instead of always sounding just as predictably lean and analytical as you would expect.
This has always been true and so to me "synergy" has always been something reserved more for things like speakers and amps or cartridges and phono stages, you know things that actually interact. As opposed to something like a power cord or speaker cable or interconnect that is going to sound the same no matter what system you put it in.
That last one of course will trigger the usual suspects. As intended. Because they ought well to be triggered. As the first step in disabusing themselves of such nonsensical notions. Which they ought well to do, for their own good if not out of consideration for all those they might lead astray.
You are right to be suspicious of the tone control or what I like to call band-aid approach to system "matching". This is as popular as it is self-defeating.
Every good power cord, interconnect, speaker cable, amp, phono stage, turntable, cartridge, you name it, that sounds really good in my system has also sounded really good everywhere else its been tried. Well, duh! That's because they're good! The crap that's not good, of course its only gonna be tolerable in certain setups- ones complimentarily flawed!
That doesn't make it "good" and neither is it "synergy" its just one set of flaws sort of compensating for another.