Sharing the results of my research thus far into account security at three brokerage houses:
PART 1 - ACCOUNT ACCESS
It seems I was a babe in the woods to think a good user name and password would actually protect my accounts at Fidelity, Wells Fargo, or even Vanguard.
It is WAY too easy for a fraudster who has obtained control over my cell number via SIM swapping or port-out fraud to click “forgot user name or password,” enter some information that I’m sure is easily obtained on the dark web (if that effort is even necessary), get my one-time 2FA code by text or call, and have full access to my accounts (locking me out in the process).
At Vanguard one of the pieces of information needed is the email they have on record, so at least I can create an obscure email address that I only use there and hope that protects me.
Fidelity allows authenticator apps and Wells Fargo offers a hardware key of some kind, but what I understood from talking to customer service is that the option to sign in using their existing 2FA systems (text or call to your phone) is not removed. Hmmm....
Vanguard again seems to be the clear winner in that you CAN remove those “basic” 2FA options (by setting up two hardware keys).
PART 2 - TRANSFERS OUT
Vanguard has some security against transferring money out. They do allow a one-time wire transfer to an account in a different name, but only by phone with the help of a rep, and the rep has to get an OK from a higher level. I can better protect myself from that by having an enhanced security password for phone access.
They said they would likely refuse a wire transfer to an account in my own name, telling me to link the account instead. They send alerts when a new external account is linked and impose a 7-10 day hold on transfers to that account.
I haven't yet researched security against transferring money out at Fidelity or Wells Fargo.