Rubbish! It's not the only way, just currently the most common and therefore accepted way. There are a number of large airlines that dont have a seniority list but still manage just fine. Ryanair would be one example.
Rubbish yourself! Equating Ryanair with a real airline job is asinine. They are the most employee-unfriendly airline out there. The only reason they had no seniority and had to hire DEC's was because of their high employee turnover! The only people who don't like a seniority list are management, mangement wannabes and Johnny-come-latelys!