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Many of the arguments predicting the A380 would not be a success are applicable to the 777X. Obviously the 777X is much smaller and much more efficient, but in the A350 and 787 it has 'competitors' that are much more flexible, barely less efficient and well-established by now. The 777X has a good customer base, but if the largest and most important customer by far wants tom reduce their orders you have to admit that the future is shaky for the 777X.
As one of the original 2 or 3 people who originally argued that the A380 did not make any business sense... you are so wrong in your statement about why those select few of us pointed out the flaws in the A380 business case were saying it did not work.
The A380 was a huge jump in capacity compared to any other aircraft: The B777-300 (which had poor and declining sales) had a published seating capacity of 396 (according to Wiki) and Skytamer says actual seating ranged between 314 and 451 seats. The B777-300ER ("W") had not yet been introduced.
The B747-400 had already seen its heyday and production was already significantly slowing. Wiki does not list an official Boeing published seating capacity for the B744; but my research indicates that it ranged from 275 on British Airways to 565 on ANA domestic routes. I've seen several mentions of the B744 with a typical 400 seats for a 3 class layout. This was an aircraft already well past its prime in sales that the A380 was targeting.
Airbus introduced a "nominal - typical" 525 seat 3 class aircraft at the very time that the nominal 400 seat aircraft (both 744 & 773) were not selling well with noticeably declining sales. Wiki says that the A380 has been configured in the range of 407 by Korean Air to 615 seats by Emirates, with the typical being in the 480-490 seat range.
This new Aircraft was also so large and heavy that most airports in the world that could accommodate a 747 or a B777-300 could not accommodate it without disrupting airport operations. An entirely new larger gate class was created. Airports typically had to spend over a $Billion to relocate taxiways, buildings, and build special gates for it.
It was quite obvious to a few of us that this new VLA only had a very restricted market slot... and that there was a limited number of city pairs that could realistically use it. I personally believe it was more of an EGO trip for Europe than anything else... and it turns out a very expensive one at that.
The B777-300ER ("W") was introduced a few years later with the same Boeing same "published" 396 seating capacity (per Wiki) with better fuel economy and range... which essentially dominated the market for the near 400 seat market (838 sales), and killed off both the A380 and B748 as well.
The B777-900 (& 800) are a modest increase in seating capacity successor to the most successful selling "large" aircraft of the last 20 years, and will have improved fuel economy. It likely will not match its predecessors sale numbers... but, its not out of place in the market like the A380 was. It does not represent a large increasing in routine passenger demand with an aircraft that requires airports to modify their base infrastructure to routinely use it as did the A380.
In fact, in my opinion it does seem to be targeted to the upper portion of the "Large" aircraft market. The A350-1000 is similarly targeted.
Have a great day,