The western banking system is much more porous than one would think. Sanctions against individuals could be a very fine grained stopgap solution.
The below is mostly writing off the recent shock of having been centimeters away from buying real estate off one of the most important known straw men laundering shady Russian and other former USSR money. I discovered his identity just in time...
A lot of this shady money was laundered through Baltic banks. Just one straw man, Staņislavs Gorins (Stanislav Gorin), was a director in name in many hundreds of companies in Latvia and offshore that laundered enormous amounts and moved it west.
He claims his identity was stolen, but that's very unlikely, given actions like him personally going to foreign embassies to help setup foreign shell companies. And given he's actively scheming with OneCoin, a shady Bulgarian crypto coin.
I went looking down the rabbit hole a bit further. It looks like Latvia has somewhat learned its lesson, but especially in the UK, relevant legislation is like Swiss cheese: one giant loophole. Just search for "companies house loopholes".