I'm not sure how anyone would expect Javik to have any insight into defeating the reapers. His entire civilization totally failed. Their only successes were basically exploited by the time he's discovered.
My point was that Javik does not add anything to the story. There isn't a single place where Javik makes a difference, where his existence as a prothean, from a storyline perspective, has anything necessary to add. He has no added value. He is just another gun, and I have already plenty of them. I didn't feel like I really learned anything new either. We witness the protheans being wiped out, something we already knew happened, and he didn't really explain much of what was going on with the crucible which he explains with a piece of dialogue about being a soldier, not a scientist. When you take him on Thessia he just hammers in what you're already learning about the asari worshiping protheans, without really adding anything of note (and we know some of his claims are even wrong, like his idea that the prothean gave the asari biotics). Great! We know since ME1 that all space-faring species are based on Prothean technology, not to mention that you will get all the relevant information on asari-prothean relationship regardless of who you bring. Even someone like James Vega, who is not familiar with the genophage, or the reason why Salarians and the Turians are disliked by the Krogan, points out that the statues in the temple look like protheans.
He intentionally tries to demoralize his fellow squad members and takes pleasure in making the people who are supposed to trust him in battle miserable. That's all he does, and I don't see how this is useful. He's basically a condescending racist and the worst part is that no one ever calls him out on it. If someone just put him in his place once in awhile I think I'd have much less of a problem with him.