You know, in your second link, the writer states that the gravity change theory is not very popular among current geologists. While as someone else pointed out, this doesn’t mean that the theory is wrong, it does cast some doubt on it, especially since science is in some ways a communal effort and validation.
In any event, interesting theory. I would wonder however whether cold-blooded versus warm-blooded differences between animals, and the complementary consideration of resource scarcity, would create enough selective pressure to weed out the large size of dinosaurs from contemporary animals. But, then, there were some very large land mammals too following the dinosaurs’ extinction. But, this is a question for a paleontologist.