Correct. That's how politics work. Maidan had no power until Right Sector joined it, and it lost power after Right Sector left Maidan to join the weak government.
In any situation, the real power is always in the hands of men with guns. The question is if there is any power that control men with guns. Men with guns went for the party that allowed them to get the most out of situation, switching sides to Maidan initially, and then to the weak government that had West's support after it became obvious that it would not survive a weak without them, allowing them to extract massive concessions from them in exchange for their support.
As for "proof", it takes living in one hell of a bubble not to see it. Clearly, Nuland telling us who will be in government weeks before the overthrow was a coincidence. McCain visiting was also a coincidence, as were several others. CIA chief visiting before the announcement of "counter terrorism operation" was also a coincidence. Kicking Klichko out of power structures, who actually wanted change is also a coincidence. Utterly absurd rhetoric coming out of Kiev today is also a coincidence. Oligarchs being installed into official posts is a coincidence. Maidan threatening "Yats" with assassination (but lacking the power to do it because Right Sector left it) after he showed them who will be in his government after the overthrow was also a coincidence. Svoboda and Right Sector getting posts like deputy of minister of freedom of speech is a coincidence. Them going on to beat up journalists in Kiev until they sign their resignations is a coincidence. Said journalists not getting their jobs back even after the Western media couldn't put a lid on that particular story is also a coincidence. And countless other coincidences you can find by following the news, and just reading carefully, as funnily enough, it's actually there in the stories a lot of time, even in the Western media. It's just well obfuscated, like the story on the Ukrainians soldiers leaving Crimea, with long moaning about how their entire families have to be uprooted. Which ends up in short sentence that those make for barely a quarter of Ukrainian troops originally stationed in the region. The rest apparently switched sides and are staying.
I have a suggestion. When the amount of coincidences reaches the point, where to believe in all of it being a coincidence starts to be smaller than that of winning a lottery, you may start considering that maybe, just maybe, you live a propaganda bubble and look utterly hilarious, not to mention gullible to those who aren't inside it.
Just something for you to consider.