Scipio Prime's shields and damage reduction buy Guan Yu the uptime his slow, heavy AoE needs, on matched infantry buffs.
Sargon adds a second infantry skill-damage lane so the march still hits hard between Guan Yu's big actives.
Ragnar Prime's troop-agnostic leadership kit adds a second skill lane while Guan Yu supplies the heavy infantry AoE.
Leonidas' defensive infantry front keeps Guan Yu alive to cycle his expensive AoE into the packed troop counts of a rally.