The proposal shows an example on how to isolate environments without duplicating some code. It acts, more or less, as a template for the architecture which you render it according to the values (environments/accounts).
I agree it isn't a simplest way to do that, but I don't think that it add as much complexity this. Perhaps it could be more laborious for the point of view of architecture, but it could be easier to handle and maintain.
Though in large part it's a challenge because we only see hints at some of the timelines, so we'd have to make guesses and leave some placeholder branches in...