I'm pretty sure the reason that Boeing didn't want to certify the Max as anything other than a 737 is that this would have required expensive pilot-retraining for all airlines purchasing that aircraft, and this would have put Boeing in a bad position relative to Airbus, with the main factor being 'fuel burn per seat' where the Airbus A320neo had an initial advantage. The plane designs are nicely compared here (2014), esp. Fig 2:

https://seekingalpha.com/article/2765285-the-battle-on-the-n...

The shoddy software primarily responsible for the Boeing 737MAX disasters was introduced so that Boeing could market the planes to airlines as a standard 737 that required no expensive pilot training programs, as far as I can tell. The nature of the FAA's regulatory process seems mostly irrelevant here, unless rushing poorly designed products with huge risk profiles to market to help Boeing improve sales is something the FAA should promote... note also that Boeing lost around $30 billion in market value over the MAX debacle, which could have been avoided by FAA being more strict, even if that mean fewer plane orders.