It really doesn't, unless you play a 6-degrees-of-separation game with synonyms. "Completely mitigates" is a nonsensical statement; mitigation, by definition, is incomplete. If it were complete, it wouldn't have been mitigated, it would have been fixed or some other term that implies finality and completeness.

Per Oxford:
1) Make (something bad) less severe, serious, or painful
1.1) Lessen the gravity of (an offence or mistake)

No other definitions are recognized. Most others (dictionaries) match or are nearly identical to the above. I cannot even find anything that gets close to your redefinition as "weakens".