I agree that it is very irritating for even average-sized rubrics. I added the following CSS as a customisation to the Essential theme to get around this problem.
/* Grading for rubrics - make the KDSC marking rubric table wide for tutors to use */ .path-mod-assign .fullwidth[data-region="grade-panel"] [data-region="grade"] { max-width:none;}
Unfortunately if you don't have administration rights, you cannot edit the customisation, but you could always ask the administrators to add it in.
If that doesn't work, and you are feeling brave, you could try opening your browser developer window (Firefox link), and adding the line in the "{ } Style Editor" tab (in Firefox). This overrides the default theme setting, and works while you have the developer window open.
Presumably it is just as irritating for students when reviewing their marks, so the following CSS fixes the issue for them.
/* Make the grade rubric wide for students to see it better */ .gradingform_rubric: width: 1300px;