9 out of 10 people agree that in a room full of 10 people one person will always disagree with the other 9.
I'm not a ST nerd, and had to look up what Species 8472 even was. After a quick read, they win by a landslide. The only thing that saved The Borg was Plot Armor Janeway. If it was purely left to just Species 8472 and The Borg without outside Plot Armor, The Borg would most assuredly be extinct by now. It wouldn't matter if The Borg assimilated the entirety of Humanity, it would just be a matter of time when you have no offense OR defense against your enemy.
The Doctor was ordered to delete himself if Voyager was assimilated and he was the only one that could replicate the nanoprobes needed, you cannot credit the Borg with anything more than firing a few torpedoes that Voyager supplied them. Crediting the Borg as the victors is like crediting Italy with winning WW2 just because they switched sides when losing.
I mean, I'm not a ST fan by any measure, but going by the wiki, your topic is a non-question.
Species 8472 was winning comfortably and close to eliminating the Borg entirely. They weren't because of the intervention of another species.
It was one of those writer things where they say "you think the borg is scary, well get a load of this." The universe is not a safe place.
.
"This will be a fight against overwhelming odds from which survival cannot be expected. We will do what damage we can."
-- Capt. Copeland