Plunder isn't what matters. Someone who only scouts and assassinates in a war, but is very active, can earn mithril just as well.
Hypothetical situation: So a 100k comb stat player does 150 actions and nets 100m bonus and gets say, 2 mythril Then a HLBC player does 150 actions and allots 3B bonus. They also earn 2 mythril?
It also depends on the opponent clan's prestige as that affects the clan's total payout. From that the individual share is worked out.