User blog comment:IamJakuhoRaikoben/Sorcerer Magazine, Issue 50: February 2016/@comment-28052271-20160325093621/@comment-7418318-20160325094719

vs. Hades
 * direct: Natsu, Lucy, Wendy, Erza, Gray
 * support: Carla, Happy, Lily (destruction of the Demon Heart)

Mard Geer
 * direct: Natsu, Gray
 * support: Lucy (without Galaxia Blade this fight would never have happened and the Spirit King likely tired Mard out a little), Sting and Rogue, but they mostly countered Jiemma showing up

As you can see the fight against Hades involved far more people than the fight against Mard Geer.

The powerscale argument is valid, but the numbers aren't.