I think there's an element of truth to the engineers' claims. Working on different code bases means there are a lot of things you would otherwise need to talk

I think there's an element of truth to the engineers' claims. Working on different code bases means there are a lot of things you would otherwise need to talk about that now you don't. It's very much the case that you still need your interfaces to be clear (in fact, clearer!) but those discussions can be somewhat isolated, so more work can proceed asynchronously. Just how isolated depends on how exact (and correct) the specifications are, which is a question of trading up-front work against interruption.