What are these other ways to protect from favoritism, brown nosing, back stabbing, nepotism, etc because in the history of the world it hasn't been accomplished.
From my experience the only people who want merit based system are people who excel at brown nosing, back stabbing and general douchebaggery.
I have extensive experience in both systems and I'll take seniority system over merit any day. It has many negatives but it also akin to SOP's for flight operations. You know what to expect and the rules and procedures are known so you can plan your life. With every merit system I've been a part of or experienced through others there isn't any stability or predictability unless you fit into douchebaggery or love to give reacharounds description.