Title. 100% Rending is trivializing armor, not to mention that Rending actually works on ~75% enemies in the game and with such amounts it notably increases damage against virtually every elite, special and boss on top of it’s intended effect against Crushers/Maulers. The ‘sister’ mechanic of Rending - Brittleness - is even hard capped at 40%.
Almost no other source of Rending/Brittleness in the game goes beyond 40% max (usually much less, 10-20%), and those that do have low uptime (like Zealot’s Fury of the Faithful) or are quirky to utilize against the armor (such as Bladed Momentum blessing on Heavy Sword).
On top of that, much less powerful blessings have been already nerfed - Blaze Away and Ceaseless Barrage for example, neither of which comes remotely close to altering the gameplay anywhere near as much as Uncanny Strike.
There are also other sources of Rending/Brittleness, such as Veteran’s Rending Strikes talent and other blessings - which Uncanny Strike in it’s current form renders entirely irrelevant. Punishing talent on Zealot has been nerfed from 30% Impact to 5% Impact for this exact reason - that it didn’t leave any room for other Impact bonuses, so the same logic should apply here.
Uncanny Strike should provide no more than 40% Rending. Weapons already have base scaling against armor types so it’s not like the heavy armor cannot be dealth with at all when not using Uncanny Strike.