If you've been playing any PvE content in SWTOR since patch 4.0 at all, you must have noticed that your companions have become significantly more powerful than they used to be. To some extent, that was to be expected, since their gear ceased to matter and back when it did, few of us kept our companions' gear up to date at all times, so they were pretty much always weaker than they could have been. Also, we were told in advance that affection/influence was going to affect companion performance in combat come KotFE time - considering that it didn't used to before, that was going to be another buff.
However, what's been going on in practice has been crazy town. Healing companions spam massive heals non-stop, to the point where your health never even moves even while you fight multiple mobs at once. Tank companions can solo seemingly everything, as they shield themselves from damage and have a small, constant self-heal going on. And as far as dps goes, someone on the forums let his max level companion parse on a dummy for five minutes and came out with about 5600 dps. The current top dps player on the worldwide leaderboard sits at 7200, so at least in that area companions have not completely taken over yet... but they are still outperforming the average damage dealer by a considerable margin.
The official forums are on fire with people discussing the issue. One side wants to see companions nerfed, the other enjoys being powerful and wants to hear none of it. Just tuck your companion away if you don't want it, they say, but leave mine alone! (Here's the currently biggest forum thread on the issue that I could find.)
Personally, I am somewhat concerned. I get that people enjoy being powerful, and I don't mind if someone wants to sit back and AFK while their companion does all the work (though personally I'd find it boring). And as someone who plays a lot of healers, I certainly appreciate my dps companions actually packing a bit of a punch now when I'm out questing. What worries me is the effect that overpowered companions are going to have on small group content.
Now, they have always been able to fill the role of an extra player in most heroic missions and flashpoints. They were not as good at the job, but you could manage in a pinch. And that was partially what they were there for! However, in my opinion they should never be preferable to having another player around, and that's exactly what I'm already seeing right now, especially with healers. A guildie of mine was in a flashpoint the other evening, they lost their healer, and when the group finder gave them a replacement he expressed disappointment because they had been doing so well with a companion healer. I've also been in a similar situation myself, when my group of one tank and three dps kept wiping on Colonel Daksh in tactical Maelstrom Prison (even with me kiting him around the boxes like a pro, all old-school hardmode style). When two people quit, me and the remaining dps whipped out our companions instead and things only got easier from there. Did I mention that they even know how to use CC properly now (unlike a lot of players)? It's not hard to imagine players getting kicked from groups in favour of someone's companion healer. This should never happen!
Under the old system, companions were good at dividing small trickle heals among multiple group members, but there was a hard cap on their burst healing, because using their biggest heal would place a debuff on the person who got healed and for several seconds they couldn't be affected by the same big heal again. (This also prevented healer stacking.) I'm not saying we need that exact same system back again, but there does need to be some kind of cap on companion performance in my opionion.
Even if we assume that people won't go to such extremes as kicking people to replace them with companions, new players will simply get a completely warped view of the way the game works. I've always liked how the companion system allowed newbies to get at least a vague idea of how trinity gameplay works and that it made it viable to level as a tank or a healer, even if you played "solo" (that is to say just with your companion) most of the time. However, the kind of output we currently see from companions will just set completely unrealistic expectations for newcomers. The first time they meet a real healer, they'll think: "Wow, they sure suck!" Because unlike their companion, a real healer has resources and cooldowns to consider and can't just spam huge heals non-stop. And why can't that tank just keep himself healed up...?
I hope that Bioware will address this in some manner. I'm willing to give it some time because I know from experience that something that looks like a problem after a big patch may sometimes sort itself out after a while, and not all bad predictions necessarily come to pass. Personally I do suspect though that companions will require at least a little bit of tweaking if they aren't supposed to replace real players in group content in the future.
NOTE: Patch 4.0.2, released on the 17th of November, did indeed nerf companions' damage and healing output. Musco explained their reasoning here.