That's quite right, yes.
Ironically, it's in MMOs like World of Warcraft or Wildstar that I found bosses matching that description, to some extent.
I say to some extent, because due to the nature of MMOs, you can find strategies to beat bosses on the internet and sometime completely miss that the game tried to prepare you all along. And sometimes, instead of thinking "hey the game prepared me to fight this boss, I saw those mechanics before!", you'd instead think "hey this quest is a training for boss X".
Anyway, thanks to quest lines, dungeons theme, or overall knowledge of the lore or ingame mechanics, you can enter a boss room and immediately get that he will do this, probably will do that, may enter a second phase where X happens, etc.
And when you're right, it's kind of very satisfying.
Funny you should mention MMOs. Me and the aforementioned friend of mine had a lot of MMO bosses in our minds when we were thinking challenging bosses. I didn't mention them because I don't know how well that can translate into a single player experience. MMO bosses not only challenge you mechanically, but also individually and as a group. That is a hard dynamic to transpose into a single player game. They have mechanics that are actually challenging to overcome and don't feel contrived (especially some bosses in WoW). It still is a predetermined script you work around but it has enough of a bite to not matter so much and it feels great to kill a boss. Though D:OS 1 has and D:OS 2 will have a co-op experience, so I say go nuts. Make optional bosses as hard as you possibly can (given my points of consideration of course).
