Google3 is a huge codebase of high quality that moves exceptionally quickly, so it just seems like your priors are getting in the way. Complaining that a large-scale change among tens of thousands of software developers requires a tool (Rosie) is sort of the same thing as all those people who complain that it's too hard to cope with having millions of machines in prod, i.e. the type of people who wash out of the company in a few months and then go on to a career of complaining about it online.