It is not unheard of even in western countries to hear about people having hundreds of cars in their name or even flats, yet receiving benefits as they declare zero income, one would think how hard this can be?
It's usually down to a lack of sharing of data or, where data is shared, non-standardized formatting of the data which makes automatic analysis impossible. There are multiple departments involved: land registry, property registry, tax authority, benefits authority, and so on.
It's also not a very high priority. Even these types of rare, extreme cases of benefits fraud are usually trivial on a national budget scale, whereas tax evasion isn't.
So yeah I'm not that convinced of how well govt handle data crossing.
The XML format provided under OECD model CRS/AEOI makes data analysis trivial.
Motivations are high to spend resources on analyzing this data. The ROI calculation is simple: are the costs of hiring analysts and/or getting software to automatically compare CRS XML data with local tax records less than the immediate and long-term gains of finding out about money hidden offshore? The tax authority doesn't need any other government body to help with this. They have everything contained within themselves. Does Person A's filed taxes line up with the reports coming in from overseas? Yes/no. If no, go to prosecute.
I would not recommend relying on a government's motivation for catching benefits fraud as an indicator for how motivated they are to catch potentially millions and billions of untaxed money. Especially if we're taking about western countries, where tax authorities are usually the most efficient and ruthless government body.
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Being that Revolut can be very trigger-happy in that department. 
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