I'd start by checking to see if there is a newer BIOS version available through ASUS, and follow that up by checking to see if ASUS has a newer chipset driver for your Zenbook as well.
When you say the temperatures don't get too high, how do you know this? Have you monitored the temps while running that multicore test and if so, what were the core temps?
Are you running the unit on a hard flat surface with nothing at all to possibly block any of the intake or exhaust vents on the bottom of the laptop?
Do you have a bunch of third party applications running that you have installed or that came preinstalled? Keep in mind, almost ALWAYS when those Cinebench and Geekbench benchmarks are achieved by those who run them and gain high scores, they are just about always using a machine that has just had a clean install of Windows done and has no other additional software installed. They are "lab clean" so that nothing is using any system resources except for Windows itself and whatever drivers are required in order for the system to operate properly.
Any other applications or utilities that you've installed, like monitoring software, overlays, mods, plugins, or anything else you've installed will likely have it's own background and tray processes running and those use system resources just like anything else, which will affect scores on top of other factors like potentially having an early BIOS or not having the latest chipset, network adapter or audio controller drivers installed. And you can't rely on Windows in most cases to supply the best drivers as those are generally vanilla universal drivers, not the full features drivers offered by the laptop or motherboard manufacturer, or the CPU manufacturer in some cases.