Earth's dominance at Dominance doesn't come from Mercs tho. It literally comes from their own exalting power. It's their ratio of active power exalters versus active peeps, which is way more favourable to getting dom than for other flights. Mainly bc Earth doesn't have a lot going for it except for its Dom Power.

And the biggest discrepancy in battles also isn't Mercs -- the main chunk of levels afaik during battles come from PB and Raffle. Mercs make up a tiny proportion.