It seems to me that Galatians 5:1-4 is clear: those who are circumcised are required to keep the whole law.
This appears to me to be a different way of salvation than what Paul preaches is for the Gentiles in Galatians 2:16; if those who are circumcised can even be saved.
(I am playing devil's advocate here to a certain extent; I am attempting to get you to think about what the scriptures really teach on these matters. Do I have an answer? I don't know that I do. But I know that there is one.)
Paul isn't saying that. He is pointing to those who seek to be justified by keeping the law and circumcision. He's really pointing to those who still seek to adhere to the old covenant. It does not mean that if one is circumcised, that they automatically forfeit being saved under Christ Jesus, which is pretty much what you're saying. All knees must bow to Christ Jesus and believe on Him to be saved. Paul taught that, so there is no salvation by keeping the law. All must go through Christ Jesus.