A big part of the problem is the training Apple gives their tech support people.
I contacted Apple tech support about six weeks ago to discuss the slowdown on my iPhone 6. At that point, the connection to the battery was being discussed widely on websites and in newspapers. But the tech support reps I spoke to had no clue about it. They wanted me to do a factory reset on my iPhone and then reinstall all my apps one at a time. That's right, they said I shouldn't restore from a backup because that could perpetuate the slowdown.
The "solution" they offered would have been a lot of work for me and it wouldn't have solved the problem. Meanwhile, anyone paying attention to Apple news knew what the problem was.
Why doesn't Apple train their AppleCare representatives on the technical causes of these common problems? Let's hope they do much better when this next update comes out. It's not rocket science.