There has been a great big discussion on why this is terrible, and should be a no-go for PvP here:
PvE wise, it sucks plain and simple, but it is more managable. I mean I use pet growl in M+ all the time if a tank needs relief for some ability or hit, or if tank DC’s for a sec etc and my pet can die from that so I enjoy the 2 sec rez to keep going after that. It would make having to use our pets as relief more of a pain because we will be out 6+ seconds of damage with GCD. It’s managable, but it just takes our viability away.