You're speaking of a hot war which isn't ever going to happen owing to nuclear weapons. And if it did happen it precludes many of your scenarios. For instance naval vessels are highly vulnerable to modern weapons technology. Aircraft carriers were constantly sunk in WW2. The main factor that shifted after WW2 is that nukes precluded direct war between major powers, so they ended up being exclusively used against places incapable of defending themselves. More generally Ukraine has provided many lessons in modern war, and among them is that experience in invading these sort of countries is not only useless but perhaps even harmful as it can contribute to flawed assumptions.

That 15% no longer has the majority of the economic power in the world, or anywhere near it. There's a great visualization of the G7 vs BRICS here. [1] That's obviously not all countries, but those omitted aren't going to change the result nor trend. Just as important is what "economy" means. When we speak of war we're referring to the ability to go from ploughshares to swords, but most of the 15% have neglected their core manufacturing competencies and transitioned to service economies where these large numbers don't really translate into economic might of the sort we might imagine. Again, yet another lesson from Ukraine.

[1] - https://www.statista.com/statistics/1412425/gdp-ppp-share-wo...