Productivity has always been inversely exponentially correlated with manpower, I don't think this is related to AI, and I don't think AI speeds anything up in this scenario. If nothing else you're now constraining what could be one-man development speed to the speed of a chat-session, which is much, much slower.
If you know what you're doing (and most times even if you don't, yet) it's much faster to work actually solo, without bothering with any AI assistance except at most something like one-line auto-complete on command.
If you know what you're doing (and most times even if you don't, yet) it's much faster to work actually solo, without bothering with any AI assistance except at most something like one-line auto-complete on command.