PayPal, Venmo, Stripe, etc -- any service provider that I choose to share bank account (or debit card) numbers with -- gets the information for a small holding account only.

I maintain the balance in that holding account around the level where I'd be "irritated but not affected" if something were to go wrong.

Honestly I just don't trust them to correctly and quickly fix any errors or exposures. So I prefer to avoid the issue altogether.

I already have a "burner" bank account for gym memberships and other non-trusted entities.

Maybe I should take a two-tier approach for business accounts, to "sweep the sweeps," so to speak, and PayPal et all only have access to a business burner.

And most banks that I'm aware of will let existing customers create new accounts with distinct routing/account numbers online.

Not in the US. Especially unique routing numbers. Maybe you mean virtual credit card numbers.

A bank will only have one or a small number of routing numbers.

My point was that most banks will let existing customers open new accounts online. This will create a new routing/account number combination that you can share with the service you don't trust enough to share your primary account with.

You can also add a (new) debit card to the new account, and some providers let you create virtual cards at will. But that's not what I was talking about.