Same boat. This phone's performance is my biggest headache right now. A factory reset is only a temporary bandaid because it slows down again almost immediately once things are up and running. Doest matter that I keep less apps installed and disable as much bloat as possible, it still slows down.
My phone will run perfectly smooth at random parts of the day, though. Usually, though, performance is average at best, often times taking a dip, then with those rare instances where it actually runs like how you'd expect a high end device to run.
And my front camera randomly stopped working so now I have an excuse to do another factory reset today.

Battery capacity is always going to matter. Battery technology improves at a slower rate than the rest of the technology in the phone that often demands more power consumption. Then you use to factor in that everyone uses their phones differently. What's considered good battery life for some people is probably bad battery life for just as many. Bigger batteries solve this problem while those who are moderate to light users get the added benefit of having their phones last even longer without needing to be charged. I'll never understand how people will literally argue against removable batteries as if carrying around a power bank or a phone charger and cable is some how more convenient than us carrying around spare batteries that are too small to even notice in our pockets.
I am dreading the day I have to rely on a power bank. Man, maybe I will just get the Moto Z2 Play.