What if we just enable oem unlock in both the system and the bootloader then use adb to push the recovery, superuser, and busybox to the system. King Root caused too many system instabilities, it had injected itself as a system app and after unrooting and uninstalling after a reboot I was left with a soft brick due to a secure boot error 1003. A stock 5.1.1 kdz and the lg flash tool was able to bring my Stylo back to life.
It could all be done by running a simple batch file bundled with everything we need for our device. Linux would probably be the better option but it could work the same in windows.
This would not work because you still would need root to push thesu binaries to system/bin. Now it might be worth trying that while you have TWRP installed as it has access to the system and has root. But if you need to use the TWRP to beable to push the su binaries why noy just flash the zip. Plus the zip does a systemless root on the device so it patches the boot.img as well when you flash it.
Know the insucure boot error you got was probably because you turned the Enable OEM unlock off in developer options and still had a custom ROM on the device like katana.