For most users, they’ll only get a prompt when they login to a new device, so the risk of notification fatigue is lessened, so I think it’s OK on that front.

I agree however that admins are constantly bombarded with alerts and can suffer from vigilance fatigue. I think there is certainly a need for a different approach for more privileged users - it could be as simple as red banner, instead of the blue theme that is common across the MS, SalesForce and Okta MFA apps.