I definitely don't think that the generalist hiring practice is the best for all purposes - just that it makes a lot of sense for the bulk of the hiring at a la

I definitely don't think that the generalist hiring practice is the best for all purposes - just that it makes a lot of sense for the bulk of the hiring at a large company, and that most the big tech companies do it. The big tech companies do also build well-crafted teams of specialists where appropriate (for instance, Google's Deep Mind team is all AI specialists). I don't know what sort of hiring process they use for those roles, but I would wager the process is a little more personalized, and also substantially more selective.