The Klingon-Cardassian Alliance already are the quadrant's major powers; with the exception of the Romulans, there's nobody else to
ask. That size, and the way they have to keep other species in leans, means they actually have a greater fleet to call upon than the Federation which, as Shawnster
pointed out, would be more militarized and could easily edge out the Federation in conventional warfare. But conventional warfare has never been key, or even slightly helpful, in bringing down the Borg, nor have the number of ships that can be thrown against them (and it's probably worth recalling that, talk of alliances aside, the Federation actually had to face down the two major Borg attacks on Earth by itself). The key has been creative, technological innovation that exploit the Borg's weaknesses as a gestalt culture. And while one might say that a society like the Federation is more open to creativity, and has more such individuals to call upon unlike the Alliance which ignores some of the best minds its subject species have to offer (though not all, as the case of MU-Jennifer showed), the truth of the matter is that, historically, innovation is not bound by moral governance, as only the recent examples of Nazi Germany and the Soviet Union point to.
Fictitiously yours, Trent Roman