Today I decided to do a clean install on MacBook Air - did an online recovery, erased the disk and installed MacOS High Sierra. Even clean it didn't behave really good so I decided to try Geekbench - with the Mac restarted and only the Geekbench app running - I got pretty low score - 1251 on single core and 2457 on multiple cores.
By a chance I had a Kali Linux (Debian) Live USB nearby so I decided to boot it and try Geekbench again. Got about three times better scores on both.
It just feels much better - runs smoother, everything feels faster... Why could that be? I'm super confused. Can anyone shed some light on my case?