Enforcing stupid & unreasonable ToS in court is a slippery slope that can be used against users.
You want to use an alternative client to export your data because the official client doesn't allow it? ToS violation and the developer of the alternative client gets sued.
Want to screen-scrape some website to automate some tedious manual behaviour? ToS violation and you get sued.
The ability to delegate some manual process (logging into online banking and getting the data) to a third-party (like Plaid) should be a right that we should defend.
At least with credential sharing & screen-scraping nobody can lock you out. Does it suck? Yeah. But I'd rather take a solution that sucks than no solution at all.
In the UK banks (in an attempt to encourage online banking) have a fraud guarantee related to losses from unauthorised access to online banking systems as long as you haven't given your credentials to a 3rd party
Screen scraping, like plaid, obviously breaks that concept.
In that case it seems reasonable for the banks to have a ToS that says "no giving your credentials to third parties".
If there's no such guarantee and the user is on their own from a fraud loss perspective then I don't see a reason for enforcing that kind of ToS.
All that said, the idea of a transactional banking system being online with purely static credentials in 2020 is scary one. Decent 2FA should be used for any system that has a financial impact.
Will be interesting to see where this goes.