The 77X is a compromise to address the top of the product range basically. As such it addresses a few key areas for Boeing.
One it puts a lot of pressure on any A380neo to go beyond just new engines and pay the full boat cost to give it a new wing and stretched fuselage. Being even bigger than the A388 making such investments would seem dubious.
Two it stripped off the part of the market that I think really needed the full 77W type capacity in the ME3 and made the unavailable to the A35K. Outside of those airlines I feel like the 789/10 can compete quite well with the A350 family. Denying Airbus high volume and likely strong margin sales to the ME3 hurts them.
Finally it’s a huge part of the program expenses are important investments in the future anyway. The large carbon fiber wing factory is a critical investment for all go forward programs. This was as good of way as any to jump start that process.
Like anything the 77X is a compromise but to me it seems a reasonably well struck one. Money is mostly being spent on areas that have long term company benefits while cost were kept in check enough that you might reasonably make some money in a space that has proven to be dangerous with both the A380 and 748.
The 777X is a compromise, influenced by the Boeing Board capping development costs very early, and in turn, the requirement to exploit grandfathering to the nth degree.
At the time of X conception, it was fashionable to distance from the 787 family. In hindsight, a new 787 wing and fuselage extension would have been more cost-effective.
The politics within Boeing would have followed a similar path to Airbus, with A330CEO management switching to A350 and then performing a reverse takeover, if the 787 birth had been trouble free. The 748 and 777 models would be winding down, there would be two 787 wing options, and an 11 and even possibly a 12.
The X certainly raises the A380NEO bar, but don't under-estimate how CEO pricing has hurt Boeing on early X sales, and the need to 'bridge' the 777 production line with below cost sales (which also delays future 787 and X sales).
Even if the X is spot on with delivery and performance, the first decade's production is crimson, to the extent Boeing would probably like a few cancellations, so they can re-sell production profitably.
The X is a culdesac, whereas further 787 developments to create the same capabilities would have been a super highway. Nonetheless Boeing will make lemonade with the X. Whether the distraction and revenue will be justified, time will tell.