I think everyone who helped make his world win its WvsW liga should get the finisher.
First, in the season description of season 1, the finisher was separated from the meta-achievement reward, therefore the conditions for getting it, should require the other.
Second, the finisher should be the reward for winning the WvsW liga, not doing some achievements that may not even help your world.
So the finisher should not come as part of the Season-Meta-achievement, but should be a reward for everyone who participated in WvsW during the season on the winning world.