Actually, the reason I didn't like her on TNG was none of the above. I didn't like that she was an interloper. Maybe introducing her was "realistic", insofar as things on Star Trek can be, since she was supposed to be some sort of "Borg expert" - I don't know, and I don't really care. All I knew was that somehow here was this stranger getting a completely undeserved leg up on Data - and especially the first viewing, when I had no idea how permanent this was going to be, I found that utterly unacceptable.
In a way, I had a quite similar feeling any time some rarely or never-before-seen Admiral was bossing Picard around .... especially if the character didn't seem too sympathetic, like Nechayev


Plus, there's just no way I could see her being more "expert" on the Borg than a cybernetic being that had been at pretty much every encounter the Federation had had with the Borg.
Perhaps no more "expert" but perhaps no less, either. She would have been someone who studied the Borg for the past 6 months as her main daily occupation. She would have been at the nexus of all Starfleet intelligence regarding the Borg. That would no doubt have included all intelligence gathered by the ENT-D, and perhaps quite a bit more (including intelligence from other species). So I would think it's quite possible she gained some insights the ent-D crew simply hadn't. And the crew would have some hands-on experience she simply hadn't. Hence she would probably still be the best possible complement to the crew under these circumstances.