I just noticed questing in Pel that my Rend "Devastating" hits do less damage than my "Critical" Rends. ~30% less damage. 16.7k vs 25k for simple 'criticals' This led me to testing other skills, and I noticed it on Blade Wall and Raging Blade.
To be more precisely, the culprit is the "Critical Damage Multiplier" weapon legacy. It boosts your critical hits, but not devastates.
Critical hits get a 50% damage bonus by default, devastates get 100% bonus. As soon as the legacy bonus exceeds 50%, your crits hit harder than your devs. When maxxed, your crits get a whopping 166% damage bonus from the legacy, meaning your crit bonus is 216%.
Other classes have crit legacies and see that effect as well, but the champ legacy has the largest bonus, so the effect is more obvious.
Edit:
Since ppl will point out: You also get a bit crit damage from passive skills here and a bit of devastate damage from relics there, so the 50% threshold isn't a fixed value. That won't change the outcome, since the weapon legacy outperforms all other bonusses combined.