Hello,
I went through this a few months ago (but on ~15k endpoints)
You could try this method (first of all You must change mcafee policy, disable password protection and self protect)
But in my case on some endpoints only mcafee agent was uninstalled, and in more then 50% cases mcafee dxl wosnt uninstalled at all and could not uninstall it manualy also)
Running mcafee endpoint product removal tool after harmony was installed fully also isnt a good idea bocouse it could coroupt some blades (antimalware goes to unknown to not running state) got info from support that it is z known issue and they will send You an patch for fixing this issue)