Planetside2. You can grind certs 24/7 and you'll have lots more option than a casual, but your character won't be appreciably more powerful than that casual's character.
And yeah, those who put in more time will always win wars by attrition. The problem is that they win all the battles by default, which isn't fun for either side. In a better system the casuals could at least go down fighting, or even win if they can field superior numbers to offset the difference between individual players' grind time.