As to the OP: Cardinal Newman was not primarily a historian. All believers should investigate their own denomination for its beginnings. We Catholics must, as we are under relentless attack from all sides. Hyperbole? Try defending Catholicism on YouTube, for example.
The vast majority of denominations are decades old and no more. The Americas are the most egregious examples of the explosion of denominations. Great theological license was taken, and is being taken, and by its very nature this produces division.
For those who are Lutheran, study Luther himself - pondering his erratic behavior and his personal damning of everyone one who disagreed with him and, IMO, that ‘should’ spur you on to look beyond Luther. The same with Calvin, Zwingli, Simons, Wycliffe, Knox, you name them. All split off and founded denominations after their private opinions differed with their brothers. Where is the truth in that?
How can a Protestant ever be certain of the truth, since innumerable versions exist within the umbrella called “protestantism.” Did Jesus teach that each of us should consult the texts and decide for ourselves? No, He did not. He - God made man - intended that an authoritative Church perpetuate the faith.
Those communities which are founded on the bible violate our Lord’s core principle. I am not saying that those who follow such beliefs are ‘bad Christians’ or do not love Christ. Most of them are very fervent lovers of Christ. It is simply that they are utterly lacking the foundation and infinite depth that the Church founded by Christ contains.