The modern age military victory is the only one in the modern age which requires some kind of strategy to full off effectively but it has a pretty big issue with it.
If I want to capture 7 enemy territories reasonably quick I would need good science and production to get higher tier troops and planes. But if you can get planes quick enough that means you got high science. So if your goal is just to win why would you even pursue a military victory when instead you can just do 4 quick projects and you don't even need to build more than launch pad?
I think to make military more viable of a win condition to pursue I feel that the science needs to have a system where each project for science is done in the backend and not in your production menu for the city. This should then be based on how many launch pads/ science buildings you have.
In my opinion culture could use a similar overhaul as it has the same problem. Why would I pursue a military or ecnonomic victory when science or culture is easier. I think you must be required to commit to a certain win condition not in a sense where you pick it from a menu at the start of a game but more where if you dont commit you won't win. At the moment there is not much stopping you from pursuing multiple victories.