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.
The unity is in love. an internal thing, not external visible things. I have unity with Mother Teresa. I do not agree with everything she says however. I have unity with Quix. I do not agree with everything he says however. I have unity with Mad Dawg. I do not agree with everything he says however. I have unity with Alamo-Girl. I have agreed with everything she has said so far to me on FR maybe someday she will say something I do not agree with but that is OK we are all a bunch of poor miserable sinners in need of a Savior.