Considering all the ridiculous changes that ZOS is toying with it seems silly to ask about something so small, but why change the cool-down of Dark Convergence for both PvE and PVP if the change dictates that the reason is to help "reduce the frequency in which it can introduce Ultimate-like effects to the battlefield."
That is obviously a PvP specific nerf, so make the nerf only active while in a PvP environment... Why change it for PvE and punish players who use the set for PvE? I built a fun set for PvE and with this change it will ruin the efficiency of the set.
ZOS consider making the change only active in PvP.