You are falling into the false trap often expressed by Protestants. You confuse “spiritual beliefs” with doctrine and dogma. Varying spiritual beliefs or theologies have been held by well-meaning Catholics on various topics over the years. Many of these spiritual beliefs, understandably, do evolve over time.
However, once a specific dogma or doctrine has been defined by the Church, either through a dogmatic Council or through papal infallibility (which was simply a theology until the First Vatican Council defined it as dogma in 1870), it can never evolve and is immutable until the end of time.
The long-held early theology that the Blessed Mother’s Glorious Assumption into heaven, was not a dogma that simply “evolved”. It was a “spiritual belief” that was eventually determined by the Church to be beyond dispute and defined as “dogma” by Pope Pius XII in 1950.
As for the Blessed Mother being declared a so-called “co-redeemer”, that has been advanced and rejected by the Church on many occasions––including at the Second Vatican Council, and later by Pope Benedict XVI. The Catholic Church teaches we have only One Redeemer, Jesus Christ.
But is certainly understandable that Protestants reject that notion of the immutability of doctrine and dogma. Indeed. if they accepted it as being the truth, they would not be Protestants, they would be faithful Catholics.
Catholics do invoke Mary as coredemtrix amongst her other titles conveyed by roman catholicism.