Setting aside that there is surely more than one cleric in many settlements, I assume exactly the constraints on clerics that the latest version of the D&D rules specify. Remove curse is on the core spell list for clerics. I suppose some gods might forbid their clerics access to it, but I cannot think of a single one that does in the normal Faerun pantheon.
I did indeed, but am reading it now avoiding any assumption of a degenerate free-for-all.
The player intent authors that the cleric casts remove curse and thus their friend does not transform into a dreadful monster at sunset, by following the written mechanics for influencing. (With the parallels I have already pointed out.)
I'm not sure what you intend here? In both cases the DC is decided by GM's perception of the circumstances plus applicable factors already stipulated. In the latest version of 5e, the DC by default is 15 or the INT of the target.
"Diplomancy" has over several editions been notorious for allowing players to help themselves to outcomes they desire, and multiple forums host discussions on how best to manage it. Acknowledging it takes the form I describe might prove fruitful in seeing ways to successfully handle it.
I'm not dismissing that there are differences, I am resisting wrongly attributing those differences.