Actually, I don't necessarily agree.
I definitely think smartphone manufacturers and software developers should've mastered battery life with FHD screens before moving on to QHD screens, but we don't live in a perfect world.
Although QHD doesn't bring any noticeable improvements to the table on smaller screens, it still keeps people happy. It's more consistent than FHD. QHD is pin sharp no matter what device you're using (unless you have a built in Tartarus in your pocket and use your television as your cellphone) while on the largest phones FHD has to start to stretch to encompass it all. Going any farther than QHD is ridiculous, and we definitely hit QHD too soon, but I think that if we had waited a few years QHD would've been perfect.