Plaid is a complete joke -- "give us your bank passwords and we'll validate your account". Banks are an even worse joke -- "20,000 logins today from one IP address, nope that's not a scam".
Plaid customers are the worst. Like Transferwise, you cannot setup a business account with them without giving Plaid your business banking passwords. What company treasurer would allow that?
Now that Visa is holding the bag this fixes two problems:
1. For customers, there is less risk that Visa will steal all your money than some "fintech" startup
2. For Plaid customers, they may realize Visa is buying this for the data and they may think of Visa as a competitor and not want to support them.
Because "just give us your sudo password to install software" and "just give us your bank password" to send money is a thing... the obvious dumber people in the future will have to do "just sign this power of attorney to create an account with us."
Banks (at least the big ones) often block aggregator traffic. This is resolved after speaking with them. The usual resolution is to whitelist specific IPs for massive traffic.