Open players outsmart/outgun open players.
Solo players outgrind solo players.
Look at the numbers. Two concurent CG attract roughlty 5000-10000 players. It is a huge number in the statistical sense. As long as the CG give no adventages to solo for one side regarding the other there no issue. The side with better mobilisation/numbers will win regarding the way you play open or not. Play the way you like it.
I'd be surprised if there is such a difference between empire/fed proportion of open/solo players. Well ED have the numbers.
If you actually consider grinding a war tactic, than there is not much i can do to help you but, wars were not won with people grinding in parallel universes(cuz they dont exist judt like they should not in ED), they were won with actual tactics and outsmarting your opponent. (Germany and Russia: Germany was mislead to attack when winter was coming. Russians knew it, they retreated and let germans advance. Once winter was there germans failed cuz they were not prepared. Outcome: Europe is now Europe not Germany