That's a pretty risky assumption, don't you think? What if that is their intention? And again, every other aircraft, western as eastern, have increased fuselage width. Even Boeing.
The MC-21 is a vanity project.
The C919 is a very serious effort, but the goal is not to compete against Western airliners on economics, but to establish a local capability to build airliners. From a strategic standpoint it makes total sense to make the most comfortable airliner, not the most efficient one, for public relations reasons. The efficiency can come in the next generation or two, once the Chinese have established that they can build, and support local examples of, a safe airliner. Only at that point will they start trying to sell outside China and compete directly with Airbus or Boeing.
Nonsense. The 777 was wider than all direct competitors, namely the A340 and MD-11. The 787 is wider than the A330 and 767. Boeing has consistently been increasing the width on its widebody offerings.
This is only right if you think the 777 and 787 were originally intended as 9Y and 8Y, respectively. Start with the 787. I believe it's clear that the 787 was intended as 9Y from day one, and that it wasn't initially marketed as such for a combination of internal political reasons and PR benefits. As a 9Y airliner, the 787 was narrower than its 9Y predecessors (777 and DC-10/MD-11).
The 777X is absolutely intended for 10Y, and like the 787 is narrower than its 10Y predecessors, including both the 747 and A380. But I'll grant you that the original 777 was intended as a wider 9Y—and that is a decision Boeing has had to undo, first by squeezing 10Y into the 777 for most operators taking new deliveries after the 787 and A350 became available to order, and then by optimizing the 777X for 10Y.
The 737 is a 1960s compromise. It has to keep the weight lower in order to remain competitive. A clean-sheet won't have to. Keep in mind, a wider fuselage also creates a tad more lift, so it isn't just increased drag that results from such a move.
I think it's clear from the experience of suboptimal fuselage widths (most prominently the 767) that additional lift doesn't make up for additional weight and drag from a wider fuselage. Engine technology is not going to provide Boeing with a major improvement over the A320neo in the foreseeable future. Particularly if NMA allows them to optimize NSA for a bit lower payload range than you see in the A321neo, I think their best route toward a competitive product is to squeeze weight ruthlessly while carrying the weight with a cutting-edge wing.
Judging from the disgruntled engineers who stepped forward just after the MAX grounding began, that isn't what they recall. Boeing indeed arrogantly tried to sell 737-800s as equals of the A320NEO, right until American Airlines decided Airbus was good enough...
Disgruntled are going to be disgruntled. They also claimed the 787 would never fly.
I remember the "737-800 has better per seat fuel consumption than A320neo" claim, the assumptions under which it was true (a mission length under 500 nm with a relatively low-density layout to maximize the per-seat effect of 12 additional seats), and the general chuckling that accompanied it. I'm sure salespeople were earnestly reciting it and putting it in slide decks, and I'm sure everyone on all sides (including the Boeing side) saw through it transparently.