Community Manager Eric Musco posted an explanation for the nerf on the forums: “What we saw in those instances is that companions, simply put, were just way too good. Their healing and damage output could be greater than that of a very skilled player with a fully maximized character.”
Yesterday Musco followed up his original post by asking players for feedback on companion performance post-4.0.2. Both threads have since racked up well over a thousand replies each, with heated discussion on both sides of the issue.
Source: Nerf explanation, feedback thread. Thanks to everyone who sent this in!
Update: Musco posted this evening that the team will be readdressing companions soon. “As we go into the weekend, we wanted you to know that we have gone through this thread, the forums, Reddit, and social media to gather everyone’s perspectives. We have come out of this with quite a few action items that we are going to take, including buffs for companions. On Monday, we are going to release a forum post highlighting our plans to address current companion balance, along with the state of heroic missions and star fortress.”