Isn't the thing about Daleks that they have never faced a credible foe, because the Doctor makes sure mankind never changes, never evolves, and never develops anything better than a 5.56mm assault rifle till the day the universe winds down? In contrast, the Borg have already faced basically every conceivable kind of foe, plus a few inconceivable ones, and persevered.
Thus, while the "infantry" in both camps wears supposedly impenetrable armor, the armor of the Borg is orders of magnitude better nevertheless. Of course, the Daleks have a very powerful anti-personnel raygun, but the Borg are accustomed to rayguns of all sorts. Funnily enough, they don't have a characteristic raygun of their own, so it remains a mystery how a Borg Drone would actually attack a Dalek warrior...
But speaking of adapting, the Daleks supposedly already know how to deal with Cybermen, while no encounter between the Borg and squat little single-person hovertanks has been reported yet.