I think that might be his excuse, but not his reasoning. I think you've addressed the reasoning in your later post, about the 4680 cells.To be honest the standard Plaid performance figures where impressive enough, which I think is Mr Musk's reasoning behind the cancellation.
I would say there would still be room for a plaid + and a roadster, 2 different types of cars with mind blowing performance and obviously quite different handling. You have Audi for instance making the R8 but then also the RS6, both great cars and very quick but coexist peacefully without cannibalising each other due to the different use cases/ types of customerMy initial thought after "aww" was that why would anyone buy the roadster if the plaid+ existed.? Plaid+ was very close to the none stupid space-X version. Now it leaves clear water between S and Roadster