The iPhone 6 was possibly the worst thing that could have happened to Samsung. It took the Galaxy S range's unique selling point and matched it. Then, in a passable attempt at an own goal, Samsung the other two big advantages of its flagship out from the S6 - removable batteries and expansion card slots.
Now I can understand why some people argue that a removable battery is not a requirement and I'm sure that Samsung themselves were aware of how many battery charging kits it sold. The truth is that removing that capability from the S6 meant it was less of a phone than the Galaxy S5. Perhaps my favourite thing about the S5 was that I never plugged it in at any time. The spare battery was always charged up and ready to be dropped into the phone at a moments notice.
Its also true that this isn't the way that most people think of the replaceable battery. Users are considering the ease of replacement when the battery loses its ability to hold a charge. If you've bought a phone on a two year contract its entirely possible that you'll be suffering from this halfway through your contract. Buying a cheap replacement battery is an easy salve for this problem.
I've yet to heard a valid argument against the memory expansion slot though.
Having now replicated the change across its whole flagship range (S6, S6 Edge, Edge+, Note 5) Samsung has nowhere left to hide. If its new device range can't reverse its recent poor performance (and I see no reasons why it should) and Apple continues to take bites out of its rivals market share, it may be time for Samsung to accept the reality that it doesn't understand its customers or the premium market quite as well as it thinks.
For me if I was looking to buy a high end Samsung phone right now I'd look no further than the Galaxy S5 / Note 4, depending on how big you want it. If many more people feel the same then Samsung's next set of results could end up being a bit of a bloodbath.