If you can't even be bothered to set up your own auth, you are obviously not a serious organization with any amount of resources. Why should anybody trust you?
> It's more secure than rolling your own auth
If you think that the two options are "use a third-party SSO" or "roll your own", you should not be running a website.
> it means we're not storing passwords
If you think having your own account system requires "storing passwords", you should not be running a website.
> We're pre-launch and focused on building the product, not reinventing authentication.
You're not supposed to "reinvent" authentication, you're just supposed to set up basic username + password auth with one of the many libraries that exist for every web framework. If you cannot handle that, you should not be running a website. It is deeply worrying that you think this is a complicated task.
(Also, if you do not understand how a basic login system works, I do *not* want my Google account anywhere *near* your slopware.)