Rage change is outright unnecessary.
Unleashed Might is already a more attractive pick for several reasons. It's there for people who don't want extra clickies or deal with crashes, it gives a much better version of Hand Clap (kd instead of kb, decent AOE dmg, and procs well), it plays better with team dmg buffs, plus it already look to be outright better than Rage is on Brutes due to Fury's effect.
Even without the added Res debuff, Rage won't be picked. The Def sets can just swap over to Unleashed Might with close to zero downsides.
If the issue is really "equitability", then make the -def and -res scales more equitable. Hell, remove the -def altogether and see how much of a difference it makes. If the issue really is double stacking Rage, then change that. Or don't change it and see it go unused anyway.
Haven't gotten to test it on my SS/Invul Brute. But I'll likely keep Rage on him anyway because I like it thematically.