Orc boys and orc big uns are pathetic and no one uses them in SP or MP.
BO are extremely cost effective and are some of the best infantry around. Savage orcs are decent too.
As a result, no one uses orc big uns or orc boyz. They get shredded by missile fire, have terrible stats which don’t hold up well with anything (even empire infantry trade cost effectively with them)
Big uns have terrible leadership and poor ap so struggle to deal with large units (supposedly their niche). In campaign, the buffs for them are pretty bad (skill trees and tech trees) so they don’t even become viable in campaign.