Well, I was trying to assume that this was an accurate recounting, and coming up with possible explanations in good faith!
Normally, when an anonymous commenter on the internet says that something is true because of a private conversation that only they were privy too, and I have not seen any other independent sourcing, I am more inclined to simply disbelieve that person.
For example-
"I was at a convention, and Joss Whedon told me that he originally wanted to replace Robert Downey Jr. with Martin Sheen as Iron Man in the Avengers!"
I would assume that the likeliest explanation, given no external corroboration, is that there was maybe some ...miscommunication or overstatement.
Now, perhaps I am wrong. I do not know everything. If you are aware of some other sourcing for your claim outside of this private conversation, please let me know! I love learning more history, and what you are saying contradicts everything that I am familiar with regarding the origin of the turn undead ability (and, for that matter, the Cleric). It also seems somewhat bizarre given that EGG had a repeated habit over decades, on and off the record, of minimizing any attribution to Tolkien, so it would seem especially odd that he would attribute something to Tolkien that others have not attributed to him, and that the extant knowledge places the ability pretty firmly with Arneson, Blackmoor, and Sir Fang. Not to mention EGG's documented dislike of the ability (which was grandfathered in from Blackmoor),
So at this point I am assuming, absent further details that I am unfamiliar with, that you either misunderstood what EGG was saying, or that one of the other reasons I listed might have happened. But, again, if I have misunderstood what I assume to be fairly well documented history (well, as well as most of this is), please enlighten me.