Your documentation says you use service providers, specifically MX and Finicity. Is that correct or are you integrating directly (or some mixture)?
Plaid, Finicity, and Yodlee all purport to support both those direct connections with big banks and the long tail of smaller banks and credit unions. It reads like Stripe has built some direct connections (where possible) and is wrapping other providers for everyone else. That is also, as I understand it, what MX does.
https://financialdataexchange.org/FDX/The-Consortium/Members...