macOS decides the order of the menu bar items not Stats - it may change after the first reboot after installing Stats. To change the order of any menu bar icon - macOS Mojave (version 10.14) and up.
I love menu bar utilities, but I hate menu bar clutter. For years, I used Bartender to keep my utility icons neat and tidy, but I wanted to try and find an alternative that was available via the App ...