OK, for every action, there's a reaction... Mr Newton's insight in the world is amazing, and it even applies to phones. You can get your 6P to have battery life more on par with the S7E, but in doing so, your 6P is going to feel a lot more like a S7E and less like a 6P. My wife has an S7 and while I can see that the 820 is a faster chip, it gets there in a bit of a sputter-y kind of way. My 6P feels a lot more fluid... nothing drastic, mind you, but there is a distinctly different feel to both phones that you notice once you use both for an extended time.
And that fluidity comes from the kernel configuration. The 6P's kernel is set up to be pretty vanilla, trying to strike a balance between system performance and power usage. Others, such as Samsung, tend to calibrate it towards reducing power usage. Now, the effect of that choice means that in certain situations, the S7's CPU will be humming along at a lower relative speed than the 6P's.... and scaling up that CPU to the speed needed for the task at hand take a little bit more time.... enough to be noticed.
So the option is there to load a custom kernel (which isn't the case for the S7 820 variant, nor may it ever be) and with a few tweaks here or there increase the amount of screen time you get by a rather sizable amount. And some enterprising types are fussing with configurations aimed to get the best of both worlds... highly customized settings that basically increase the responsiveness of the CPU.... so you get reduced power usage without the hit on day to day, light duty performance.
Or... you leave well enough alone. The 6P's mileage is well past my own personal usage point (i.e the amount of time I typically use it in a day) So I don't have any battery anxiety. The way I see it is that if a phone is at that point, worrying about it's ranking in an arbitrary test isn't really worth it.