As per all multiverse crossover NRPs, how do you plan on balancing it without having it be limited or constrained in such a way which takes away from the feel of the nation?

Star Trek vs LOTR won't mesh well as would many fictional Nations. Westeros vs the NCR would be a curbstomp more or less. The Imperium of Man can basically kill anything in sheer numbers. The city in Attack on Titan will never hold against the likes of something like Empire of the Rising Sun. And the GRM would be powerless in the face of the Galactic Empire.