Yeah I don't want to spoiler for anyone so don't click the hidden bit unless you've already completed the Trials of Shar. But you're right, I
spoiler
successfully persuaded the super-hench devil (that I'd been repeatedly warned to avoid because they're so powerful) to first kill all his henchmen, then kill himself, fight avoided
Act 2 has some awesome chances to bypass boss fights entirely... if you can pass multiple conversation checks in a row. My rogue almost won the bar conversation, but when you need to succeed 6 times in a row, luck is just not on your side.
I am just on the way to the city now (second playthrough, but the first ended at an earlier point due to my shitty choices lol), and I've made maybe half the foes I could talk to just do themselves in. Although, technically, one of those didn't take and I still had a big fight to deal with...
It's not that OP if you're playing on the hardest difficulty. On the first two, charming or even using detect thoughts on someone in dialogue only gives the bonuses. If you're on the hardest difficulty, you can piss them off when they notice you using magic on them.
On Tactician I persuaded a certain ambushing demon (devil? Something) to kill all of his allies and then himself, completely dodging what is otherwise a pretty tough fight.