Healing is down, but not 75% down. Companion heals and hp are down about 25-30%. Running a heroic star fortress (voss) I did notice for the first time since the expansion that my healer companion healed for less than 4 digits. There were some ticks in the 800-900 range. The star fortress run, I was only able to see a difference on the robot guard boss guy. The one that gets assembled then summons packs of 4 robots. If you don't interrupt the summon or go kill the adds, they were able to out dps the companion heals after about 12 of them appeared. Prior to the patch, you could just stand there and beat the boss and ignore all mechanics and easily win. Now I have to run the marauder over and kill the adds if I miss an interrupt or I can get overwhelmed before downing the boss. Better gear and I know I can ignore it all again.

The final boss I couldn't tell there had been an adjustment. Just standing there with my back to the wall to avoid getting knocked off the platform and ignoring all mechanics, never saw hp dip below 85%. This was the same as it was prior. It probably takes longer to get healed to full, but your full by the time the next big hit comes anyway so it doesn't matter.

I don't have a max level companion, but the patch notes say they pretty much get all their power back by influence 50. I run an immortal juggernaut and a carnage marauder, so I can't comment on how well the companions tanked previously. I also don't run them in DPS mode so no idea if that's been adjusted either.

You may want to swap out the companions. Some just don't work well as compared to others. Lt. Pierce sucked compared to the octopus-head sith lady for example. That imperial archaeologist guy from Yavin heals very well.