On the other hand, I also have a 13" 2015 MBP[1]. It is only ever plugged in when it needs charging. I bought it specifically for it's size and battery life, because, as ludicrous as this might sound, I want my laptop to be as portable as possible. I don't _want_ it to be plugged in and I don't want to feel like I've been working out when I've been carrying it.
I know, this is crazy talk, but might I suggest that many of the people complaining are doing so simply because they bought the wrong tool for the job? It sounds to me like an awful lot of the complainers would have been better served by an actual desktop computer.
[1] I had never even used OSX before, and own no other Apple products, but I bought a MBP based entirely on battery life and size, because it was the best option out there.