Did you figure it out? If not, you may want to try choosing "All processes, hierarchically" from the View menu in Activity Monitor.

I "solved" the problem by restoring a week old backup from before I'd upgraded to Sierra. All other things were equal, so the OS was the culprit. This is why good backups are important, never know when Apple's gonna screw you.

Man I feel like I'm attacking apple a lot recently but this is something else I saw on my MBA - various daemons (powerd, kernel_task, accountsd, and more I can't remember) spinning on 100% cpu usage leaving the laptop unusable.

The browser takes up most of takes up most of my resources. Apart from that it would be Adobe products and sometimes MATLAB (all less resources than safari). My terminal would be negligible.

I agree with your comment. Generally, OSX often means I am using more resources to do the same task than when I use my archlinux. But in the era of 16g+ ram and terabyte Harddisks, I find it simpler to just let OSX use extra resources so I can spend less time thinking about low level processes.

Your OS manages all of your memory. You can't get any memory at all without asking it for it. How much memory were you requesting, and why didn't you get it? Is that the problem you were solving? Is there some reason you suspect the OS preferentially gives memory to web browsers?