I'm horrified by the notion of banks in particular storing their data where "those datasets are not well governed, no-one knows the schemas". This is people's money you're talking about.

A lot of applications can fail with an "eh, whatcha gonna do?" shrug when records fall out because their schemas drifted or two different developers interpreted them differently. So somebody's preferences stop working or their early "likes" get forgotten; so what? Move fast, break stuff, etc.

But when your data actually matters, I'd much rather pay the expense of having some discipline about it. The idea that my money might become the stuff that gets "broken" is kinda terrifying.