Yes it is true that insulting a group of people will generally not result in helpful responses from those very people.
It's also true that there are individuals who get their identity tied up with their choice of brand and can't tolerate any negative comments. Just as it is true that there are some individuals who stupidly make sweeping negative generalizations based on the actions of some individuals and then expect anything helpful.
Odd that you're seeing such a difference in behavior between the Air2 and iphone6. You were right to try getting the iphone6 replaced as that behavior suggested faulty hardware. Have you done the training bit where you go into Settings->TouchID&Passcode and keep applying your finger/thumb? Not by adding a finger, but just at the setting screen touch you finger and see which of the fingerprints gets highlighted indicating a successful read. It's claimed that doing this a few times at different edges/angles helps fill in gaps and enhance the reliability.
My experience with TouchID on the 5S and 6 has been quite solid. Most of the time any failure is directly my fault in terms of not really having my thumb on the home button. I can't recall enough instances of it not working to estimate a success/failure ratio. That doesn't mean others don't have an issue, but is merely an example of one person for whom it works well.