You bring up a good point on CASM, which is true if, and only if, your market allows you to fill the airplane at reasonable ticket prices.
As the market trends towards long range point to point service, the -380 is dying because its size forces it to serve only on trunk routes, while the 787 is making sales records because it can expand into all the long range point to point service, e.g. Denver - Tokyo, in addition to flying regular routes.
Finally, while the A-380 claims to beat the 747 CASM by 15-20%, the 787 claims to beat the 777 by about 20%, making it even better than the -380...I've not seen a head to head comparison of 787 vs. 380, but all of the technology on the 787, including ancillary systems architecture, that saves fuel, is absent from the 380.
Now, the 350 looks to be a great airplane, with many enhancements to put it on a par with the 787 for efficiency, but while serving a 777 size market.
Also, the 350 met design goals, production dates, and performance specs. Initial reports are that it's an impressive airplane.