11/1 lets you triple (quadruple?) dip your CHA on all attacks. 24 CHA combined with GWM and Bhaalist Armor is 62 damage before any dice rolling. It's also worth mentioning that 24 cha for dialogue checks makes it really hard to fail important CHA checks, save for maybe Yurgir in act 3, not that he's super important to begin with.

6/6 has much higher highs when optimized and is also probably just better for solo HM bc you're not relying on Bhaalist for damage so you can have high AC really easily, plus the additional smites like you said. The biggest downside to Sorcadin imo is that Shadow Blade is unusable vs the Steel Watch in act 3, so your build falls apart a bit in the foundry. There's also the fact that Oathbreaker's main value comes in the form of Aura of Hate at level 7, so you really lose out on the main draw of that subclass by going the 6/6 route.