I don't think that Protestants disagree on the essentials. Here's an example of a basic confession which unites many protestants -
Reforming Catholic Confession
Also, 99% of Protestants accept the Apostles' Creed. What's expressed in that Creed is, in my opinion, the absolute essentials. We are very united on these things. We're divided on other things but I would say that these are non-essential. But that's nothing unique to Protestants. Catholics are also very "divided" within Catholicism.
A good example of non-essential things. Baptism is essential. All agree to that. But mode of baptism? Psht. Who cares?
Confessions exist because they are very helpful. They don't add anything to Scripture. Rather, they draw out what is already implicit in Scripture. Confessions help unify the church and clarify doctrine. But confessions are not infallible. And they have no authority to add anything to the Bible.
The teaching of the magisterium, on the other hand, is taken to be infallible. They also add doctrines for acceptance that are not taught in Scripture. The difference between Catholicism and Reformed faith is not that one has confessions and the other does not. The difference is in how we view our confessions.
Non-essential items. You'll find these disagreements within Catholicism too.