As stated above- I did find the account number, but Etsy would not accept it. The bank would mail me an audit of the account with all of the statements, but again, with the account number redacted.
I did get Etsy support page to load and sent an email. They got back to me quickly and manually removed the old account number. They asked for the last 4 numbers of the current bank account listed on finances, the current payout balance and a description of the draft listings.
With regards why they require the old account number, intent is fine but it isn't a particularly secure or effective solution for ID verification. I'd argue that Etsy normalizing bank account number as ID verification just helps phishing attackers to steal not only login info but bank account numbers. Imagine a fake email from Etsy claiming that a user's bank account has been change. It links to a fake Etsy login page where it steals their ID and password, then a fake copy of the Etsy payment methods page. You want users to say "that's weird, why would it ask for my bank account number?" then look at the URL, say oh this is fake, let me go change my login info on the real site immediately. You DON'T want them to say "right, that's normal Etsy needs my bank account number to verify who I am," and give that up to a low-effort phishing attack and leave the fake site thinking all is well.
Ebay allows you to remove a bank account and holds payments until a new one is added. It required test deposits and sent multiple emails confirming the change. Stripe allows you to simply edit the account number and routing number, but uses proper hardware 2FA, and also sent multiple emails confirming the change.
There are other, more secure options. Hardware 2FA, email or phone 2FA, even security questions, would be more secure. The fact it failed and required a support contact could have been a more effective verification process but the things they asked for are all things that anyone with access to the Etsy account can already see. They even provided links to the pages in the Etsy account where I could look it up.
