I agree with your opening sentence and the frustration on the lack of finishing. I also agree that the contract extension may well prove to be a 'monumental error'.
However, I'm not sure on the factual accuracy of whether this team 'could have been developed 18mths to 2yrs ago'.
Let's rewind 18-24mths. Of the starting XV last weekend, with the exception of Hill and Stuart (who were in the squad but not starting), the rest of the pack were regular or at least pretty regular starters for England. In the backs, JvP and Freeman had barely played a game for their clubs, Steward hadn't played many more and no-one had heard of Porter. Also, even as a massive fan of Marcus Smith, he wasn't ready to start for England then. On current form, you could argue he still isn't. Bench wise, Chessum and Arundell have only just broken through and being brutally honest, Will Joseph hasn't even done that. In short, there's no realistic way you could have picked this side back then.