I think you've just argued yourself out of a position of "it depends." This is one of the few areas where there's no wiggle room. A worthy business co-founder MUST be able to bring something practical to the table, and in my experience as it also seems to be yours, there's only really two ways they can do so:

- Be great at customer acquisition (or at least as the original article says, bring in a "customer waitlist")

- Have or bring in actual funding

If the business co-founder can't even bring one of these two things to the table, there is no justification whatsoever for them to hold a meaningful share of the startup's ownership.