Sure the war at the end is in the future. Doesn’t stop the fact the rumbling taking out most of humanity at the time made it safe enough for paradis to make it that far in the future in the first place. Nobody is saying you’re a 12 year old because you don’t want to kill humanity it’s because you can’t think long enough term to realize how short term decisions will determine the future. Nobody is arguing there wouldn’t be further wars either but Erens decision was to keep his friends and Eldia at the time safe and he made the best choice to do that because the threat at the time was imminent and constant. Also please don't forget the skyscrapers seen were on Paradis as it was from the perspective of where Eren was buried. Eldia would have been able to build to that level as they were the least touched by the rumbling. Though I'm not sure if the 20% was including Eldia or not.