"The sun always existed" was the "destructive idea" that CJRT referenced in a number of places in HoME. It's certainly not as simplistic as saying "the sun always existed, get over it, move on" - and it's incredibly disingenuous to imply so.
If nothing else, consider everything that would need to be rewritten to support it:
- The Myth of the Lamps
- The Sleep of Yavanna
- The Myth of the Trees
- The first reckoning of Time
- The Darkening of Valinor
- The Myth of the Sun and the Moon
- Remind me what's so special about these Silmaril things again, anyway?
- Etc.
- Oh, and the Change of the World at the end of the Second Age; including everything about the Straight Path to Valinor.
And these were never rewritten.
Whichever way you slice it, you're going to need to handwave away
something.
So which is easier to handwave away? Some oblique references, some of which came in via subsequent edits or editions, and most of which can be easily explained away? Or
the entire first half of the Silmarillion? And so much other important stuff?
Nope, not buying it. Tolkien may have had intentions towards rewriting everything, but the key thing is:
he never did. Ultimately all that we're left with is the latest completed cosmology, and, despite some offhand references and subsequent edits, that is the Cosmology.