On 28 February 2014, newly-appointed Ukrainian Minister of Defense Ihor Tenyukh briefed the members of Ukraine’s National Security Council on the state of the armed forces during Russia’s ongoing annexation of Crimea. The picture he painted was bleak by all accounts, and devoid of reassurances, empty or otherwise. Speaking plainly, he informed the assembled members that Ukraine effectively had no military – recently ousted President Yanukovych and his entourage had systematically destroyed it during their tenure. Ukraine could perhaps call upon a total of five thousand capable soldiers from all of the units in Ukraine in a fight against Russia over Crimea.
Before the war when I speculated on how Ukraine could counter-attack a Russian invasion, I did say that my post was a paper exercise and that Ukraine's military was probably not capable of executing a counter-attack.
Sadly I was right about that. And you don't need to make up sophisticated "hybrid war" nonsense to explain a Russian victory over that kind of defending force.