My understanding is that, without MCAS or some other design change to fix its unacceptble handling characteristics near the stall, the 737 MAX would have been uncertifiable even as a new type. It is the way that Boeing went about implementing that fix, in an attempt to avoid an additional training requirement, that has caused all the trouble.
Let's be clear here, though: it's the airlines who refuse to buy an aircraft with additional training requirements. Pilots can only fly one aircraft type, and retraining to a different type is an expensive proposition. If Boeing could make an aircraft that fit under the 737 type, they really had no choice but to do it.
They also probably could have succeeded, too, if not for other systemic problems within the company.
It is not clear to me that they probably could have succeeded in satisfying all these conflicting goals, if not for other systemic problems in the company. Even now, with (one hopes) everything in the open and the systemic problems pushed aside, they are having trouble getting it done.
You say Boeing had no choice, but one choice was to acknowledge the problems, aim to keep the type certification with additional training, and negotiate with its potential customers on that basis. There is no law of mankind or nature that says Boeing is entitled to a certain number of sales at a particular profit.
