How close is the published The Silmarillion to JRRT's Silmarillion?

[Aiwendil]

Originally Posted by Alfirin

Tolkien always wanted to re-write the Hobbit and the Lord of the Rings so that they would themselves be more like the Silmarillion

That's not entirely true. He was actually much more focused on re-writing the Silmarillion material to match The Lord of the Rings rather than the other way around. As far as I know, he had no plans to extensively revise The Lord of the Rings - he did make a few minor changes for the second edition, and if he had lived longer, it's possible that further small changes would have been made; but during his lifetime he did not contemplate major changes (or at least, left no record of such contemplation).

He did at one point intend to completely re-write The Hobbit, and he wrote a few chapters of the revision, which were published in Rateliff's The History of the Hobbit. But in the end he decided against such a major revision, and instead made only minor changes subsequently.