not sure if I'm understanding what you are comparing with. what is your alternative?

if we are taking authz as a need in your org and also a single point of failure for your entire services (as you said in your comment), are you suggesting you would instead build / host your own Zanzibar like authz service, and that your in-house solution would do better in terms of availability than this external solution?

leaving aside how much you'd lose on productivity, I would guess your in-house solution will break more unless you spend a lot of time making that a highly available service (and you'd depend on other SaaS for that as well, which may also break).