They are credited as writers on Rings of Power. https://m.imdb.com/title/tt7631058/fullcredits/writer
The estate didn't pick anyone. Amazon did. However the estate might have had input since they did say that Mr. Jackson couldn't be involved even as a consultant on scripts. The show runners haven't pushed it all on the audience. The hate and other silly stuff over diversity sure. But they have admitted that things in Season 1 didn't work out as they had hopped.
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It also has to be considered that they didn't use Annatar because they couldn't use anything mentioned in the Silmarillion. They might have been able to get special permission from the estate for some things but it would be far easier to create a new character then work with a limited character. It has nothing to do with hubris and doing better than Tolkien. It has everything to do with the complication of rights and the estate being super protective of the work that was not published by J.R.R.