Loomis holds the title of GM, but he doesn't behave like a traditional GM. He oversees the inner workings and communicates with Lauscha and Benson. Talent evaluation and acquisition is deferred to Loomis and Ireland. Contracts are run by Harley. Loomis is the guy that Benson trusts so he holds the title.
You know what changes if they make Ireland the GM tomorrow? He has to order new business cards. Other than that, his job won't change from what he's already doing.
Loomis and Lauscha would need new cards too, just to facilitate the new letters jumbled to describe new job titles while everyone goes back to the same office to do the same job.