@XianShetsu Here in lies the biggest problem with these forums, people comment, while well intended, but have zero idea about which they speak.
What are you keeping in check? Invasions are simply just an annoyance, they keep nothing in check. On my server Valhalla, all the top Companies, mine included are stacked with lvl 60 players. Having 50 of our 100 players sign up for an invasion defense is simply us spending 30 minutes defending than out farming.
But dont forget anyone can sign up, so typically there is 200 players minimum who sign up to help defend, and since you can’t actually win unless the invasion gets bugged, you are really just signing up to smash NPC’s and earn 630 gold for you troubles.
Once again, what are you keeping in check? Its a bugged annoyance, nothing more, with nothing beneficial actually coming from it other than downgrading your town to take yet more gold to rebuild.
To your theory, if we have a war on the same day and time, we take our top 50 players to the war, let the rest defend the invasion, and fill any empty spots with random players. You can’t actually loose your territory due to an Invasion, so once again, its simply an annoyance, nothing more.
More to your theory of keeping things in check, I am in a war 3 days a week minimum, either in my own territory or helping another Company, but either way, invasions are not doing anything to keep stronger factions in check. All fractions help their own, and while I can only speak for team Green, we usually try to put the best Green players on the server in each and every war, regards of which Company they belong to help. So a war might have 8 - 10 different Companies involved than just the ones attacking or defending.