-The Overmind's full line is "the greatness of her spirit has been left to her; that the Swarms might benefit from her fierce example. Fear not her designs, for she is bound to me as intimately as any Cerebrate." Now I doubt that Kerrigan was bound to the Overmind to the same extent as cerebrates were (see QoB and the epilogue text of SC1), but the phrase "greatness of her spirit" is, in my mind, indicative of her ability in combat, determination, savagery, etc. These aren't really features of a full personality, but more aspects that can be just as easily used to negative ends as positive ones.
-Kerrigan never relished in killing bar Rumm, and she had every reason to hate him. It states in the manual that Kerrigan never embraced the darker aspects of her nature, and in SC1 she routinely expresses disgust at the use of psi emitters, and the mass bloodshed they will cause. This isn't the kind of person that is going to kill for enjoyment. There's far too large a jump between terran Kerrigan and QoB Kerrigan to attribute that to a character willingly undergoing the change.
-Raynor's assertion doesn't hold merit of its own. I can just as easily point out his statement of "that wasn't you, Sarah," in regards to her statement that "I slaughtered millions as the Queen of Blades..." (which is no doubt being used as evidence that they are indeed one and the same). A character saying anything about anything is always going to be within the context of their own viewpoint. At the time, no, we had no reason to suspect that anything of the old Sarah Kerrigan lay within the Queen of Blades at that moment in time*, so I can't fault Raynor for making that statement. What I will also say however, is the notion that they were the same individual in terms of persona. There was no character buildup to her becoming the QoB, and while I can get behind the idea that the Overmind drew out traits that were already there, it's still a case of implanting a new body, new mindset, etc. onto another human being. A mindset that apparently didn't fully kick in until very late in the cycle given that Kerrigan called out to Raynor while inside the chrysalis.
*As in, we get two hints in BW, and the ending of "TC" is one of them. Poor Jimmy didn't stay around long enough.