No, even if everyone else is a liar, God will always do what he says. As the Scriptures say about him, "You will be proved right in what you say, and you will win when people accuse you."
When we do wrong, that shows more clearly that God is right. So can we say that God does wrong when he punishes us? (That's the way some people think.)
It would be the same to say, "We should do evil so that good will come." Many people criticize us, saying that's what we teach. They are wrong, and they should be condemned for saying that.
So are we Jews better than other people? No, we have already said that those who are Jews, as well as those who are not Jews, are the same. They are all guilty of sin.
But God has a way to make people right, and it has nothing to do with the law. He has now shown us that new way, which the law and the prophets told us about.
God gave Jesus as a way to forgive people's sins through their faith in him. God can forgive them because the blood sacrifice of Jesus pays for their sins. God gave Jesus to show that he always does what is right and fair. He was right in the past when he was patient and did not punish people for their sins. And in our own time he still does what is right. God worked all this out in a way that allows him to judge people fairly and still make right any person who has faith in Jesus.
So do we have any reason to boast about ourselves? No reason at all. And why not? Because we are depending on the way of faith, not on what we have done in following the law.