The purpose of peer review is to identify incorrect theories and throw them out.
Not even that much, really. You can't generally detect an incorrect theory in a paper you're reviewing.
Basically peer review can only ensure that the authors have done their homework, are aware of all the other relevant literature, explain themselves clearly, thought of obvious problems and alternative explanations, and don't invoke any logical fallacies.
In practice a lot of it gets dedicated to a grad student who can't even do that much.