PvE people coming to the PvP section and are confused why this is a PvP thread. Have no clue but just keep pushing that post counter

As for the question why melee should do countdowns. It really comes down to how experienced one player is. If I see the melee or ranged have no idea about who to burst or keep bursting into defensives after the third countdown, then I will take over as tank.
When I play melee it can get pretty hectic and it's hard to keep track of everything important but I would not want my ranged to do the countdown because I'm not sure if I will be in range in time nor if I (and the WAR - assuming there's one) will be able to apply debuffs to boost my damage.