phoroforit significantly increases medic skill. people only stand still for arrows because bad medics can't hit players who are moving. i can tell u if u can arrow ur teammates without them calling for one, it doesn't slow the game down at all.
it increases meds skillset slightly by having to aim a bit/be able to predict movement a bit but on the other hand it lowers it a lot by streamlining the skill of managing and keeping track your teams health by providing massive bursts of hp at request
also these arrows "prevent" frags from happening so by ops theory it slows the game down