El Capitan is buggy, dumb, who's to blame?

Question

macOS

I bought a poppy book air 2015 (13 inches), I was not overjoyed - not a single stick, everything works quickly, no need
to reboot. Updated to ElCapitan.. updated.. Horror.. Like on Windows.. Applications do not start (for example, notes do not start at all - reboot helps).. Everything slows down... The kernel_task process loads the percent, so that the battery flies away.. In general, hell..
Why could this happen? Is the OS itself like this? Or do they say it's better to put it clean? If not one or the other, how can I return to the state in which the beech was when I bought it?

Answer 1

With a probability of 99%, a clean reinstall of El Capitan will help you. Since in fact El Capitan should work much better and more responsive than Yosemite. I speak from my own experience, I updated my iMac and Macbook to El Capitan at home and everything went fine.
How to perform a clean install: one , two , three .