[mooreds]

> The cognitive overload of having to align PM’s, ops, internal support, etc with a custom solution is worth any of the downsides.

That's a great point. You can just point at the IdP and say "this is what a user is, this is what a group is" and have the discussion wrapped up quickly. You're basically front-loading the user entity definition discussion to the evaluation phase (or, if your org has already chosen, offloading it to previously vetted solutions).