The oligarchs you refer to are the same ones that were propping up Putin’s puppet, Viktor Yanukovich. After Yanukovich hightailed it to Russia, one notable oligarch, Firtash, helped finance Russia’s invasion of Crimea.
These are the oligarchs the Ukrainians are tired of.
There are others as well....not so sure two of them who are currently bidding for Pres. and seemingly favorites to win... are the best choices...both have served under Yanukovich regardless of where they stand...and both are elites with plenty of moo-lah to spend on an election. Neither are clean of Gov. corruption....but then look at our own!