Boros Aggro brings fast, high-power threats like Magmatic Hellkite, Nova Hellkite, and Sarkhan-fueled dragons, so Erode is efficient removal that answers their biggest flying threats before they take over the game. Cathar Commando trades up in combat against their small creatures and can destroy equipment or enchantments they bring in. Goldmeadow Nomad and Aunt May are too small to block profitably against their aggressive curve of 3/x and 4/x fliers, so they come out for more impactful interaction; the lifegain shell (Case of the Uneaten Feast, Lunar Convocation, Amalia) is crucial here to stay ahead on life against their race plan, so none of it moves.