Let Greeks be Greeks, and Women what they are. Men have precedency and still excel;
Finally, our speaker lets the Greeks drop. She doesn't have to beat her opponents, nor does she want to (although maybe she's given us a hint that she could if she felt like it). She's willing to let men be first ("have precedency") and to outdo women ("excel").
It is but vain unjustly to wage war.
She decides it would be useless ("vain") and unjust to fight a battle with men for some kind of blue ribbon in poetry. Fighting isn't the point here. Like she said at the beginning, she'll leave war to the men. Um, thanks?
Men can do best, and Women know it well. Preeminence in all and each is yours;
Finally, she's willing to admit that men are the best, and she claims that all women know this fact. It's a peacemaking move.
By letting men have first place ("Preeminence"), she's helping the guys who criticize her to feel less threatened, and also fitting in with the conventions for how women in her society are expected to speak and behave.
Also, check out the switch to "yours" in line 40. The poem up to this point has been about men and their ideas. Now she's talking directly to them. It's just one more way she ups the intensity as the poem draws to a close. Can you feel it rising, Shmoopers?
Yet grant some small acknowledgement of ours.
Still, if she's going to back off her counter-attack, she wants something in return. She wants men, secure in being first, to acknowledge that women can do good work, too.
There's a little bit of poetry judo here—suddenly, by backing off, she makes her opponents look like creeps for attacking her.
What gentleman—the reader might ask himself—would feel threatened by a lady, especially if she promised she wasn't trying to step on his toes?
This ain't exactly feminism but, in Bradstreet's world, it's a pretty savvy and impressive move.