The Churches of the reformation disagree on relatively minor issues, like siblings in any family. However, we are unified in Jesus, we all saved by Grace only, thru Faith only, in Christ only. We are not concerned with carbon copy uniformity on issues where the bible is silent or vague. Non essentials are..... not essential.
I do agree with that somewhat, but notice you had to use a qualifier which shows that there are protestants outside of what people call, “mainline” or “mainstream” beliefs.
What is non essential to you may not be to another. Who decides what is essential and what is not.
And what I see coming is a time when we all will have to choose, there are some so called reformed churches that are venturing into some very troubling waters.
When those waves hit, people either succumb to heresy or break off to form another church.
Protestants are not unified.