In my opinion Patch-in-gerrit is a distinct stage in the life cycle of a bug, and deserves its own status.
A patch-in-gerrit does not mean the same thing as assigned. Assigned bugs are being worked on by someone. There work may or may not be publically visible yet. They are probably not at the stage where they want review of their work so far on the bug (obviously there are exceptions to that for complex bugs), etc.
A patch-in-gerrit does mean that there is a fix for the bug available. It has not been reviewed yet. It needs people to test the patch/review/comment. It does not mean the bug is fixed (and definitely not deployed, but I agree that is a different discussion). If I downloaded a nightly version of MediaWiki the patch is not there. Some people may want to look for bugs with pending patches. At the very least, many people would want to know that there's a pending patch when bugzilla is displaying the list of bugs in the search window.
In different life stages of a bug, different types of love need to be given to a bug. Thus the different stages should get different statuses.
tl;dr /me really likes Andre's plan.
p.s. This is not the first time this has come up - https://www.mediawiki.org/wiki/Thread:Talk:Git/Workflow/Bugzilla
-- -Bawolff