It's almost as if people are assuming, "Omg, if the Borg can't assimilate this cowboy, then their durability is tissue paper and their weapons are spitballs!" If Starfleet engineers can come up with ways to combat the Dominion, the Borg certainly can. .
I think the assumption that because a combined Federation, Romulan, Klingon and (eventually) Cardassian alliance defeated the Dominion means the Borg would wipe the floor with them is equally flawed.
Nevermind that the Dominion were cut off from their homebase because of friggen Gods.