I can see the point in pay progression (using only the military pattern) where someone long time serving in the rank will have gathered, and hopefully use, their wealth of experience gained through time.
Looking at officers pay, I believe the AFPRB set progression limits based on expected time in the rank. For instance after, I think 6 years, a flt lt could expect to be promoted to sqn ldr or have topped at his rank/time experience level.
In earlier days a Cranwell flt lt on the General List had his pay progression frozen at the 6 year point. A Supplementary List officer, who was expected to retire at no later that age 38 we granted pay progression each year. When that was abandoned and we all reached full scale at the 6 year point I benefited by jumping some 12 years worth
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That CS now no longer earn pay progression (and I see it was not wholesale across all Ministries) might seem equable or unjust depending on how you look at it. On one course we had a brand new direct-entry D-grade CS, so brand new he blushed when he had to answer a question. No way was he worth the same salary as a long serving D-grade CS. I would call that unjust.