Why does Chrome have much better performance in rendering 3D graphics than Safari?
Overall, the Etrecheck report looks pretty good. I would suggest that you remove the adware it found, as that can sometimes affect performance. You could click the red "remove" button next to items that are labeled as adware.

An alternative way to remove adware is by downloading Malwarebytes for Mac. After you do that, I would also suggest you update Flash Player just to protect against malware that may reduce browsing performance, among other things.

I would suggest that after this you also boot your Mac in Safe Mode. Once your system boots and displays a red "Safe Mode" label at the top right of the login screen, you can shut down and power on the machine. After that, hopefully things run a bit better. You can learn more about safe mode here: Use safe mode to isolate issues with your Mac