Dumbing down the Books

[Eurytus]

As I'm sure someone has said before, Tolkien wrote LOTR to create a 'legend' for England, as he believed it did not have any great old stories that were truly English. (Even the Legend of Arthur was not truly English)
This is why he wrote it in the style we see.

PS In my view, who says Sam, Frodo and all did not help Bilbo write the fellowship (up to the council) while they were at rivendell. And in my view who says Sam or his descendants did not update the book?

As to your fist point, seriously unless you can find a quotation to support this then you cannot make that point. Tolkien wrote the Book of Lost Tales as a mythology for England and had somewhat abandoned the idea by the time he was tidying up the Silmarillion, hence the vanishing of concepts like Tol Erressa being the British Isles.
The LOTR was simply NOT written as a mythology for the UK. Sorry but it simply is not true. It was written, at the request of his publisher as a sequel to the Hobbit. The fact he started to ape the style of the Silmarillion by the half way point does not change this.

As to the latter point. Sorry but you are simply making suppositions to support your defence of the style change. The book makes it pretty clear that when Frodo hands the book to Sam it is nearly complete. Can you see Sam editing his beloved master’s words? No, not easy is it.
However it is attempted to be justified, Tolkien wanted the book to appear as written by the Hobbits. The greater proportion of this was by Frodo. The style changes GREATLY and inexplicably.