some remarks about military strategy
The same amount of incompetence was demonstrated during invasion of Georgia in 2008.
Never assume evil where stupidity will do.
Interesting theory and worth raising. However in this case, I think it's unlikely. From what I read, there is no set of elite soldiers waiting in the wings. There is a shortage of young men in Russia now, unlike in WW2 where there were too many. And it is estimated that Russia has deployed a significant percent of it's total available military by now. And they are having to recruit in Syria etc.
I don't agree with a core assumption here. I don't see a motive for Putin to start this war in the first place. "... conquer the rest of the world" is rather silly, right? I try to put myself into Putins shoes: he's probably the richest man on the planet. Over the years, he has eliminated all his enemies in Russia and bent the law to his needs. Why would he risk it all .. for what? World domination? He was practically untouchable in Russia. Today's leaders can't be compared to those of the early 20th century. The Nazis were so successful because their leaders were actually fighting for an idea, a vision - however terrible those ideas were. And Putin is surely not an ideologue.
To me, it's much more interesting to analyze why Western media has hyped up this war so much and tried to escalate the situation as much as possible... Those senators demanding to send American troops to Ukraine. Et cetera. To me this felt too coordinated to just be about senators chasing clout or news corps making money on bad news.
So far both US and Russian elites have profited from this war - at the expense of Europe, the US middle class and Ukraine, obviously. From there it's rather easy to construct various theories...