That sounds more like 'frustrating' than 'challenging' when the only factor that bars you from a pleasant run is 'how stupid my cohealer is/whoever presses the mits in the party'.

Most of things becomes moot when one plays it safe by choosing to pump out 1 or 2 safety GCD heals to account for these types of players instead of casting Glaroilficosis, which only needs a pair of watchful eyes, something that a healer is normally already accustomed to. So again, where's the challenge to that?