If there isn't a consensus, is there a textbook or set of books that could shed the most light possible on the subject matter that Gums Germs and Steel attempts to cover?
I just mentioned it as part of an answer to a different post, but Ecological Imperialism by Alfred Crosby (the guy who invented the term "Columbian Exchange") is basically the better history version of what GGS tries to do, even though Crosby's book was published about 10 years earlier.
It's less focused on causes than on consequences, namely how Europeans shaped the ecologies of the regions they encountered, sometimes unintentionally, but often very much intentionally.
1491 and 1493 by Charles Mann have been cited a few times in this sub. They're not strictly "better GGS", but do go over the more modern understanding of pre and post Columbian contact in a way that most readers can understand.