I'm referring to this Wendover Productions video - The Economics That Made Boeing Build The 737 Max.
The creator asserts that designing a new long range narrow body plane would be more expensive than modifying an existing design, which is uncontroversial enough.
But he also makes the claim (timestamp 6:13) that there was pressure from American Airlines to provide a re-engined 737 over a new model, because existing American Airline pilots are already trained to use the 737.
Pilots are generally trained to operate just one type of aircraft. Some fly the a380, some fly the 777, some fly the a320, and some fly the 737, but they don't fly the 737-700 or the 737-800 or the 737-900, they fly the 737 airplane as a whole.
Pilots are trained to the aircraft, not the specific aircraft variant.
In general, pilots can and do switch between variants of aircraft even in any given day and are not required to do any substantial training to be certified on different aircraft variants.
Crucially, the FAA has never required that 737 pilots complete any simulator training before flying new 737 variants.
That's because a 50 year-old 737 more or less flies like a 1 year-old 737.
American [Airlines] wanted a refreshed 737 over a new plane since they already had thousands of trained and certified 737 pilots.
They had no pilots for a hypothetical new narrow-body Boeing and the cost of training their pilots to a new plane would be massive.
Is this characterisation correct, or is there some nuance missing here?
The thing that I'm finding a little hard to understand, is that these different variants of aircraft must have different handling characteristics, or different things to consider (ie. things unique to doing a longer flight), it does seem a bit crazy that no training would be required.
It also seems that the economic incentives are a bit backward - this kind of dynamic would stiffle aircraft innovation as a whole.