With over 31000 piwik user accounts, and growing, we're finding that the user management page isn't really scaling very well for us.
Thank you for creating the issue. I can imagine this is not usable. We hope to improve the user manager usability in https://github.com/piwik/piwik/issues/8119 and https://github.com/piwik/piwik/issues/6187 . I will leave this issue open so we don't forget it when working on #6187 or maybe we can work on this sooner.
A quick improvement would be adding a "add user button" at the top of the list, so one doesn't need to scroll down.