As a manga reader, when all this happened, I was always of the opinion that Eren and Paradis could have been much more precise and diplomatic about their war with the rest of the world. Since they have access to the Founding titan, Paradis has access to the rumbling and can use it as a deterring force. Marley loses its position as the world's sole superpower. If Paradis remained a closed off country until they managed to establish diplomatic relations with the rest of the world then full on war could be avoided, especially since there seems to be pro Eldian sympathizers amongst foreign diplomats (as seen from the Asian lady who protected Udo during the party). Not to say war isn't avoidable, but that it would be much more akin to a cold war than an actual World War.
Paradis is also well fortified and self subsistent as a nation. The only improvements they would need are anti air capabilities, which they obviously have been improving on considering they have at least one airship.
It's a slower much more passive approach which is antithetical to Eren's approach ever since he was a kid. Even though Eren seems to be a lot more collected and thorough than when he was kid, the same impulses that drove him as a kid still drive him now. Which shows that he's still kind of a twat, just a smart one.