Couple things...
A) This limited to Marvel? Everyone's only been bringing in Marvel stuff, but it was never really specified.
B) Who qualifies as "cosmic heroes"? Silver Surfer? Genis Vell? Gladiator? And if Glads comes, does he bring the rest of the Shiar with him? Depending on how wide a range we're talking here, the earthers should have a massive numbers advantage.
I'm also going to disagree with some of Khan's points...
Reed doesn't have the UN anymore, and in reality, definitely shouldn't be able to get it again in 24 hours.
Odin and Zeus aren't "heroes"... They're not evil, but they aren't really heroes either. And if anything, I'd say they belong on the cosmics team, as neither is technically from Earth anyway.
Omega mutants are cool, but wouldn't most of THEM be cosmic heroes? (I mean the other Phoenixes) Heck, even Jean probably SHOULD be considered a "cosmic" hero, as her base of operations is at the universal level nowadays. (though she would never oppose Earth)
And as to Apocalypse... Well, first off, he sucks. Second, he isn't a hero, by any stretch of the word.
So eliminating all bad guys... Cosmics should get a solid curbstomp in Marvel, depending on the pools we're drawing from here. Earth's only hope would be Doctor Strange and Sentry, but the cosmics should, by their very definition, get all of the Phoenix hosts, Silver Surfer, Glads, Adam Warlock, Genis Vell, and potentially a LOT more. And I don't even know if Strange's spells and summonings would work, because if the Vishanti are allowed here at all, they're definitely working against Stephen. And, despite LP's best efforts, he really has nothing to stop Surfer from going back in time and making the car crash do its freaking job.
Amen.