@BananikYT - As soon as I saw your ThrottleStop screenshot I wondered if this was an Asus laptop.
Not sure what the "engineers" at Asus were thinking. The Intel default thermal throttling temperature for an 8750H processor and most any Intel processor is 100°C. Asus wanted to create the illusion of a cool running laptop so they low balled the thermal throttling temperature down to 88°C. That is what PROCHOT 88°C means on the main screen of ThrottleStop. You cannot get maximum performance out of an Intel CPU in a laptop when you limit it like this. All you will get is constant thermal throttling. Sound familiar?
Have a look in the ThrottleStop Options window on the right side. The PROCHOT Offset variable is what controls this. Asus has set this to 12 which forces the CPU to thermal throttle at 88°C instead of the Intel rated 100°C. If you see a lock icon near this setting, that means the BIOS has locked this and it cannot be changed. You are stuck with 88°C. If you do not see a lock icon, you can lower the PROCHOT offset value down to about 3 which is more typical for laptops. This will bring the thermal throttling temperature up to 97°C. This is perfectly safe for an Intel CPU. I did not engineer your laptop so I cannot guarantee that raising the thermal throttling temperature will be safe for your overall laptop. I am fairly sure that Asus locks this setting so you might not be able to make this choice.
I finally looked at your log file and noticed constant PL2 power limit throttling at only 22W or less. This is a few more strikes against Asus. The 8750H has a 45W TDP rating from Intel. In the ThrottleStop TPL window, try clearing the Disable Power Limit Control box. This will allow ThrottleStop to maintain the MSR power limits. Unfortunately there is a third set of power limits managed internally by Asus that ThrottleStop does not have access to. If these power limits are set low, which they appear to be, there is no way to fix this problem. Are you running any Asus power or fan control software? Some software like this might have a cool and quiet setting. This is achieved by reducing the power limits to a ridiculously low level. Constant power limit throttling is the cheap way to create a cool running laptop. Constant power limit throttling when lightly loaded or idle really stinks. That is what PL2 in the log file means.
how big of a variance of core temps to be considered as normal?
When the cores are equally loaded, I would say within 10°C is normal. The temperature sensors that Intel uses are not 100% accurate. Intel typically uses sensors that are only accurate to +/- 5°C. It is possible for one sensor on one core to read a little high and the core beside it to read a little low even when the actual core temperatures are equal.
You also have to be careful when testing to make sure the cores are equally loaded. You can have a much bigger temperature variation if one core is doing a lot more work compared to one that is mostly idle. During a game, all cores are rarely or never equally loaded. If you do not like the variation that you see, all you can do is try replacing the thermal paste and see if it makes any difference. It might not.