They were wrong, very wrong, to include it.
I get it that there was only a handful of Borg, but they were 24th century Borg, surely they would have done far more damage and had a much greater effect on the 22nd century. Also, having Phlox's "immunity" to assimilation was a joke and far too convenient (plus had the boffins at Starfleet Intelligence, who obviously kept this whole thing quiet, knew the Denobulans had such an advantage over the Borg why weren't they developing that immunity for two hundred years, ready to provide every Starfleet ship/base with a hypo to prevent assimilation when the Borg finally showed up again?).
It's a poor example of taking an established Trek race and cramming them into the new series without any thought or finesse, as they did with the Ferengi and Klingons. I'm surprised they never brought Q in for another appearance.
Commander Austin Harris, First Officer, Deep Space Nine (by FltCpt. Bossco)
8.01 - Darkest Before Dawn
(Chapter 8 added, 12/09/2015)