Does it seem weird to our friend that every single gemara he quoted talks about the tzadikim davening on our behalf? Not a single place in chazal, rishonim or achronim say you can daven to a tzadik so that HE could help you, rather that he should daven for you to Hashem, the only one to whom prayer is suitable.
And even still, many rishonim held the halacha is not like that, and that you cannot speak to tzadikim at all; in this regard, there are different minhagim, each valid.