Please use parameter "OWNERSHIP_STATE=2" in your command to install . It will set Reader as default PDF handler for all existing users on machine.
New Command to install will be : msiexec /i "AcroRead.msi" /q TRANSFORMS="AcroRead.mst" OWNERSHIP_STATE=2 /L* "%temp%\Acrobat Reader DC install.log".
For existing users on machine ownership will be in effect only when they sign out and sign in again after Installation.
But it looks like an issue from Windows 10 side for new users (Created after installation) .