Simply put. Christ and Messiah are not the same despite them being used interchangeably.
The OT even called Cyrus Messiah, Cyrus was a mere mortal thus Paul's using Christ for God Himself must be of a greater meaning.
This shows that the historical Jewish understanding is that messiah is in no way the same as the Christian understanding of Christ.
That's why there has been messiah cyrus, bar kochba, sabbati tzvi, jakob frank, and the chabad rebbe. But there's been only one Jesus Christ.
Also all the things that the OT messiah is to be is often inaccurate for Christ, He wasn't a warlord or a king (they rejected him) or a temple builder HE did not place emphasis on any sort of Jewishness other than to reach the Jews with the Gospel.
Excellent