As to statements by CT or the Estate, note that on the dust jacket of Tolkien’s The Fall of Arthur it is stated: “The Fall of Arthur, the only venture by J.R.R. Tolkien into the legends of Arthur King of Britain ...”. This entirely ignores “Sir Gawain and the Green Knight” in J. R. R. Tolkien’s Sir Gawain and the Green Knight: Pearl: Sir Orfeo.
Jacket blurbs come from the publisher, not the author; and Tolkien's
Gawain was just a translation of a 14th-c poem, not an original work.
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It might be relevant to hear what Guy Kay had to say about the process of constructing the Silmarillion, and CT's intentions. When GK came aboard, CT's plan had been to present the Silmarillion material in keeping with the sentiment he expressed in the excerpt given above from "The War of the Jewels"- that the work
is its history, in a way, and what CT envisioned at that time was something like UT:
"The initial idea had been to produce a scholarly text rather than a single narrative. Such a book would have been some 1300 pages long, and would have consisted of chapters which had as their main text the latest version of the passage concerned, followed by appendices giving variant readings from other, earlier versions, complete with an editorial apparatus of footnotes and comments on dates and inconsistencies, and so on. The first two chapters had already been drafted by Christopher Tolkien in this academic style when Kay started work. However, Kay felt strongly that such an approach was the wrong one ..."
It was in great part Kay who convinced him to make a "synthetic" Silmarillion for publication, and I get the feeling that CT has always had nagging doubts about having agreed to do so.