99% credit goes to @squabbi for teaching how to patch files yourself and @XCnathan32 for discovering the fix itself.
1% for me for making the script .
THIS PROCESS WIPES ALL YOUR DATA AND PROBABLY YOUR WARRANTY TOO! USE WITH CAUTION! I AM NOT RESPONSIBLE IF YOU BRICK YOUR PHONE!
THIS PROCESS WILL MAKE YOUR PHONE SLOWER (6P 2 times slower, 5X 1.5 times slower)! PLEASE USE ONLY AS A LAST RESORT!
PLEASE CONTACT YOUR WARRANTY TO TRY AND GET A REPLACEMENT BEFORE PROCEEDING!
What does the fix do?
The problem with those phones are the cores of the Cortex A57, and they need to be disabled.
What should you do?
Before proceeding, make sure you have OEM Unlocking enabled on your device, or the flashing won't work!
1. Download the zip below
2. Extract the zip
3. Extract the boot.img from the image you've downloaded (the script explains how to do it if you don't know how) to the folder you've downloaded
4. Open "Script.bat"
You should also download a factory image from this link (unless you live in Japan, don't download the Softbank versions, and unless you live in Australia, don't download the Telstra versions):
6P - https://developers.google.com/android/images#angler
5X - https://developers.google.com/android/images#bullhead
The script itself was not tested, but the method did work on my 5X so it should work.
If you have any requests, you can comment them here, and maybe I'll add them. One day.
I do plan on adding TWRP, Elemental X and Magisk patching one day, and if there will be many requests that day will come earlier.
Links to original posts and videos