I’d first like to note that you have yet to define “Moral Decline” for me, as I asked. I’ll assume that means you’ve rescinded your own prior question which prompted the request.
Nextly, while the prior meanings and academic usages of a word do matter in their own regards, current common usage trumps predecent in essentially every case. Most people do not use decadent to fortell the downfall of society - although they do use it to at least imply or hint at morally repulsive behavior, in that extreme excesses of luxury in a world where people still starve to death is pretty universally decried as amoral. Then again, people also use the word to describe how a thick chocolate cake tastes, so don’t read too much into that.
Also, avoid basing your definitions off of Capitalized Names of Movements, Theories, or Schools of Thought - this is frequently a recipe for disaster, as such names need not actually be fitting in any regard to the usage or meaning of the word they borrow. Great examples include “Objectivism”, which is far from objective; “Socialism” with a basis in the word “social” so vague as to be meaningless; and “Modernism” which is no longer new, contemporary, or “modern”. There are many others like them, in similar categories and degrees of unfittingness.
But what’s truly, truly stupid about all this? Whatever word the Russian separatists actually used in the justification of their forcible seizure of private property, we can be pretty darn sure it wasn’t “decadence”, because the statement was almost certainly not issued in English.
It had to be translated, which is a very imprecise sort of thing in which meaning and nuance can easily be lost or twisted without any ill intent on the part of the translator. Who translated the statement? I dunno. Go find out and ask them why they chose “decadence” over other possible words, if you like.
