By the time that his father sold the rights of these two
books there was nothing that Christopher
Tolkien could do to change how the studios would use the stories that they bought.
I don't think though, and the article doesn't say, that Tolkien sold all the different kinds of copyright. The intellectual property right for instance can't be sold as far as I know, so the book and the story will always have to be attributed to
J.R.R. Tolkien and that is the reason why the studio and the production company were forced to pay the 7.5% of their profits. Because they had to use the name of the original author as otherwise they wouldn't be able to sell the movies.
According to wikipedia now just the LOTR films brought to the production company $2,917,506,956. The 7.5% of these ( without the merchandising and all else) is 216,705,521. The
Hobbit series brought similar profits to the company so the Tolkien Estate probably got another 200+ millions from the other three movies without calculating again the same percentage on the profits from the merchandising and whatever else they sold.
I assume that the Tolkien Estate wouldn't sell the rights of LOTR and The Hobbit books, but on the other hand the amount of money it got was close to the amount of money that J.K Rowling got for the Harry Potter movies. So I think that the arrangement turned out fine for Tolkien's Estate and in expanse for the
Tolkien family and though Christopher Tolkien isn't a fan of the movies he has no reason to complain any more for the decisions of his father.