I would venture that time in grade/service and doing the right schools and jobs are part of “merit”. You are definitely right, though, that needing a bit of pull to get into those schools and jobs is unfair.
I agree with you that Mel might do better by carefully choosing her words, but she hasn’t yet had the benefit of 22 years in service. Does the army provide leadership training to NCO’s when they get bumped up to positions that need it? Does it include the subtleties we’re discussing? If not, maybe it should consider it. I doubt that Mel is trying to antagonize Roz - she probably just needs a little help in smoothing out the rough edges.
It’s probably not too easy to remember your manners, or to be aware of how your words will be taken, when you’re flat on your back trying to fix a helicopter in the desert heat, with the thought of snipers always in the back of your mind…