(How did the Borg figure in "The Wounded"? Are you thinking of some other episode?)
Picard can't press the Cardassians because Starfleet, weakened after Wolf 359, can't afford to fight another war, even against such a relatively minor power.
Oh, and the Borg's Achilles heel was introduced at the end of BOBW I--it was Locutus himself. I thought--in Star Trek terms (which has to take us back to the status quos by the nature of the show; it's built into the dramatic DNA)--the resolution was rather elegant. FC is what did the Borg in (I'll give the execrable "Descent" a pass since those weren't "real" Borg). And I enjoyed FC. Really, all TNG needed to do after BOBW was to say "space is vast and the Borg are busy in it--they may not return for years but they will return." The Borg work best as a Sword of Damocles, like that asteroid strike/magnetic pole shift/big California earthquake we are currently overdue for.
I do see your point, though.