Re-installing Windows back to the factory version using Lenovo One Key Recovery should solve any corrupt bootloader or bootrec issues. Using the built-in Lenovo wipe on the laptop is a legitimate way to reinstall Windows and should not cause any issues with your bootloader.
Regarding the statement about data loss, it's saying that if you want to restore your system to a previous state using Lenovo OneKey Recovery, you will lose any data that is on the system drive. So, if you have any important files, such as documents, pictures or videos, on your laptop's hard drive, you should back them up before restoring the system.
In summary, you should not have any issues with your bootloader after using Lenovo OneKey Recovery to reinstall...