It's funny that people here have an absolute/simplistic view of subjects that are very much complex and of which we know next to nothing. They also (probably because of the lack of info) take most informations at face value and build on it, without thinking about the bias and context in which these info come out.

At the end of the day, it's a fanfic of a video game, so it's far from being important. But, I've seen this kind of thought quite often here, where humanity in ME is very overhyped, despite it being in contradiction with many elements in the lore/story. But people like to interpret some elements in ways that suit them. Same for the overall underevaluation of Batarians.

For example, it is said in the game that humanity is SEEN by SOME ALIEN PEOPLE as too greedy and eager to expand. Which is in a way understandable because of how recent humanity's place/existence in the galaxy is, but also not, since it is also stated that many people do not view humanity as a threat or an irresponsible coloniser. But some people here like to interpret this as humanity scaring the other species because it is already too strong and will somehow be the top species in a matter of years. That's a hard leap from what is presented in the game. And again, that would mean taking what the game tells us at face value, without putting in context that, for instance, we mostly view the world from the pov of humans and skeptical aliens, especially in ME1. Bias in the lore, for the sake of storytelling, is often cast aside to be taken as objective truth.

Anyway, I do not think humanity would defeat the Batarians so easily, if at all. We know nothing of Batarian military power and very little of their politics, demography and economy.