Protestants would argue that some of the sources of Catholic tradition were not under Jesus' inspiration. I'm sure a survey of papal history would find most if not all Catholics agreeing that not everyone speaking for the church was doing so under the inspiration of the Spirit. Others, while they may have been Godly men, also taught things (such as Limbo) which have later been discounted by the Pope.
Scripture's message has been constant.
Where Catholic doctrine seems to veer away from Scripture, or where some apparition somewhere causes Catholics to develop a particular doctrine or practice than those found in Scripture, Protestants will differ.
Protestants will also see Catholicism as essentially a religion based on faith PLUS works for salvation. Protestants will say faith alone. SOLA FIDE, SOLA GRATIA. SOLOS CHRISTOS. SOLA SCRIPTURA. Thats the essential definition of Protestantism. Take away the SOLA part of these concepts and add church membership, baptismal regeneration, and a few other things and you have Catholicism.
The Church is comprised of fallible men, we agree. Only few of what has been taught by them has been elevated to the status of dogma.
Scripture's message has been constant
The text has been constant, except Luther hacked off some books and also some laughable translations are offered as dispositive. The interpretation of the text has varied greatly and continues to vary among the Protestants.
Protestants will say faith alone. SOLA FIDE, SOLA GRATIA. SOLOS CHRISTOS. SOLA SCRIPTURA. Thats the essential definition of Protestantism.
I know, and none of it was the teaching of the Church for 15 centuries. Most of it also contradicts scripture mo matter how you interpret it. Read for example James 2 and get back to me on Sola Fide. Or show me where Sola Scriptura is in the scripture.