This is pretty lame BS. I am literally right in the middle of building a public web app (also for a bank) that does not have any sort of arbitrary user agent constraints.

As long as your browser supports reasonably-modern things like flexbox and media queries, my app is just going to work on your machine. Even if it doesn't support these things, I don't see any reason to artificially get in the way of something you might otherwise be able to string along regardless.

I roll 100% vanilla JS/CSS these days so that I can avoid getting entrapped in the kinds of hells that likely entrapped these mbna web developers. It is quite possible they use some JS framework that has a tight dependency on a certain cohort of browser vendors & versions.