The truths about Mary are important because they are still truth, since they are based in the Bible. But they are not central to the primary gospel message of our salvation through Jesus Christ.
As an example of the basic gospel message without Mary, we have only to look at the writings of Paul. In Pauline theology, Mary is mentioned only once, and not even by name.
Galatians 4:4
But when the fullness of time had
come, God sent his Son, born of
a woman, born under the law, ...