At times, the way Sisko spoke, it sounded unnatural. His delivery had a weird cadence, especially when the Sisko was angry. At those moments it did seem like Brooks was overacting, in an attempt to put emphasis on a point that he wanted to convey to the audience or other characters.
That didn't bother me, though. After a short while, you get used to it. It is what it is. Sisko's manner of speaking is kind of quirky, but quirky isn't a bad thing. It can be amusing.
Often times, when I see Picard on the tv screen, it seems to me that Sir Patrick is putting on a Shakespearean acting clinic. Like I said, it is what it is. Just enjoy it for what it's worth.