Obviously in some cases a junior developer is a better investment if it's a straight up choice.

Actually I think it'll be rare for a manager to be choosing between either a junior developer or a coding assistant, since each are going to benefit the team in very different ways and it'll often be obvious which you need.

What I mean is that at the price levels in the article the coding agent still had a realistic chance of positive ROI. People will pay for things with positive ROI.