The quality of being disproportional; the state of lacking proper proportion or balance.
From disproportional + -ness (noun suffix). This creates an abstract noun describing the quality of being disproportional.
English loves synonyms—we have disproportionality AND disproportionalness, which means the same thing, yet both show up in serious writing because different writers prefer different suffix styles.
Complete word intelligence in one call. Free tier — 50 lookups/day.