Gould is doing this for a rhetorical reason and to show that he is not biased against Broca. By talking about how "meticulous" Broca's work was, he is telling us that he is not simply blind to any good that can be said of Broca. Instead, he is telling us, he is willing to admit that there are ways in which Broca is a good scientist.
Rhetorically, this is a strong strategy as well. Gould is pointing out the good in Broca's work so as to make it seem all the more devastating when he points out the bad. He is making us think that Broca is great. He is saying that his work seemed "invulnerable" and that he did things in a "meticulous" way. This builds Broca up in our minds, making it seem more effective when Gould says, in effect, "Broca seemed great BUT here's what's wrong with his work..."