Sorry. The analogy doesn't fly. Nothing was added. Tradition always was. Sacred Scripture/Sacred Tradition. All part of the Depoit of th Faith. But nice try though.
But that is classic begging the question, circular reasoning. We have a shared entry point in Scripture for the basics of the doctrines such as the Trinity, for one example, which is why virtually all Protestant denominations that adopt Scripture as their primary source accept that doctrine.
Transubstantiation, OTOH, was not a part of that "early deposit," not in the form finally put under the protection Trent, which was the full-orbed Aquinian inversion of Aristotle's accidence versus substance, which has no traceable roots prior to Radbertus, a 9th Century monk.
BTW, it will be insufficient to raise the general idea of "real presence" as a substitute for transubstantiation. We may argue whether John 6 is best viewed as describing a metaphor for belief in Christ, per Peter's confession at the end of the chapter, but it is beyond all dispute that there is nothing in the text that even remotely supports the Aristotelian/Aquinian sophistry that empowered the sacerdotal system of later Rome, dissent from which would draw the ire of Trent.
So consider this analogy. Human DNA is the "book" that governs the development of the human organism over it's entire life span. It contains all data necessary to make a human. It does not have, in itself, all physical supplies, such as food, water, etc., that contribute to the proper growth of the person, but it has all the information necessary to make good use of those resources.
Now a tumor comes along. How does the tumor get there? After all, it does grow out of the original human material, and indeed can show by "cellular succession" that it came from the most important stem cells in the body's history.
But something is clearly wrong. The DNA has mutated. It is not the same as the original DNA. New information has been added, and old information lost. It begins to make millions of copies of the mutant cells, and becomes a serious threat to the well-being of the original human organism.
Which is why Elsie's picture (as profoundly disturbing as it is) is so much to the point. Rome and Protestantism are not in conflict except where Rome has proffered doctrines that are materially different from the original DNA of the body of Christ, as recorded faithfully for us in Scripture. The proper method for dealing with such novelties is to challenge them based on the record of that original DNA. This was the method of Athanasius, in defending, against all comers, the deity of Christ against the Arian mutation.
So your statement that "nothing was added" incurs a burden. If you say it wasn't added, you have to show it's originality, and to do that, you have to use the original reference "DNA." Otherwise the "body" has no defense whatsoever against ANYbody coming along and claiming their "novelty doctrine" was always there, just undocumented. To open such a door is to destroy the body's immunity to any new cancer.
So we Protestant will continue to stand firm, like Athanasius, for checking all claims of doctrinal "enhancements" against the book that defines our DNA as believers. You can speculate all you like, but you cannot bind the Christian conscience to anything that is not indisputably the word of God.