Yeah thats has more to do with iOS tho rather than device power. Saying the iPhone 6 is underpowered comes of as like Apple released a phone below specs. This is simply not true, the A8 was and still is at the top of the food chain.
Apple is clearly struggling with iOS performance since 7 and I just dont know what they are doing. For example I had the ios 9 beta 3-5 on my iPad Air 2 and was well happy with it (apart from the fact that animations once again have to finish before doing anything). Than I installed the GM on my phone and it was pretty bad, lag wise. I obviously upgraded to the public realise the other day and most of the lag I had is gone. Most of it tho and not all of it, I just dont know why nobody there sees these issues. iOS basically chokes every now and than and since iOS 7 they just cannot get that sorted. Sometimes its better like iOS 7.1, iOS 8.4, sometimes its worse like iOS 7.0, 8.0 - 8.3 or now ios 9.
iOS and OS X teams must also be different I suppose and the OS X team should get some credit this year. OS X is absolutely amazing imo, they did a great job with ElCapitan in all aspects.
Its not like iOS 9 crashes all the time like 7.0 or 8.0 did, and they actually fixed bugs that were over 1.5 years old but they just cannot get that smoothness right.
I think Tim Cook needs to summon his inner Steve Jobs once and a while and just go crazy. Have a meeting with the iOS team and be like "What is iOS supposed to be?". Than tell them that "smoothness" is one of them and that their work is s***t.
Or they need to hire more people because they cannot keep up with what they are doing anymore. I mean watch os, tv OS, iOS 8-9, OS X Yosemite redesign / El Capitan, apple music, IPL, Continuity, iCloud drive, much better spotlight, proactivity, handoff, siri improvements, apple Pay, news app etc. They have done a lot those last 2 years.
The answer is probably both.
How is the apple outside world? Im curious too but not because I want to leave apple.