You already have all that you need: a TM backup of volumes, you can use it from Mojave's Utilities Migration Assistant, if you launch clicking continue it will bring you back to the Welcome Screen letting you choose the way of transfer, in your case from a time machine backup.
All explained better than me right here:
https://support.apple.com/en-us/HT204350
Sincerely I will keep an High Sierra installation until the Mojave Golden Master release, but I have to admin that Mojave beta 4 seems enough stable.
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Maybe the "mv" didn't replaced recursively, anyway to avoid the reinstall, booting from your Mojave disk in single user mode (CMD+S) try these steps:
mount -uw /
rm -R /System/Library/PrivateFrameworks/CoreBrightness.framework/Versions/A/CoreBrightness
cp -R /Users/YourUsername/CoreBrightness-backup/CoreBrightness.framework/Versions/A/ /System/Library/PrivateFrameworks/CoreBrightness.framework/Versions/A/
reboot
Give it a try.