I’m curious what the cost/benefit of this would be?

I actually prefer having my accounts tied to Apple as it makes it very easy to sign in as well as keep all of my info updated.

I have a passkey tied to my foundation account but I would much prefer to have it tied to my Apple ID as that would keep my login details from being lost or forgotten and at the very least, keep all of my info synced to one place.

You can encrypt your iCloud backup if that’s what some would consider a negative of having your info tied to your AppleID.