I think saying it's been "in development" since Nier Automata gives an inaccurate connotation. It was not 5 years of production. The article goes out of it's way to say that plans started before Nier Automata started development. That to me indicates that Astral Chain was created as a concept for a new action IP for Nintendo, then was put on hold while the team worked on different Platinum titles (mostly on Automata), then came back to fulfill their obligations.
All in all, production time was probably only 2-2.5 years.
That sounds about right, and I got the same thing vibe from the article. Perhaps I need to word the title better.