No, I didn't mean that there should be no ranks - just that there shouldn't be too many.
For example... the US Army has
nine enlisted ranks and eleven officer ranks. Private (E-1), Private (E-2), Private First Class (E-3) are kind of redundant, and have no functional difference other than pay grade, usually reflecting time in service. Likewise, Specialist (E-4) and Corporal (E-4) have slight differences, going back to a split in technical & combat specialties; also the Corporal is a non-commissioned officer, while the Specialist is not. Also, at some time between WW II and the 80's, there were Technical Sergeant ranks with the same equivalence to the E-5 through E-7 (or E-8) NCO ranks, with the split between technicians & combat arms. Overall, a lot of complicated stuff.
In the sci-fi books I mentioned, I believe Pournelle had his mercenary legion (with the historical lineage of coming from a joint US-USSR combined force, with heavy leanings from the Foreign Legion) simplified down. I think it went something like Recruit (raw rookie, no combat experience), Veteren (recruit after 1 battle), Corporal, Sergeant, etc. As I had said, he also did an essay at one time, about how the current (circa 1980's) US Army had about 20% leadership positions, which he felt was too many.
So what I originally meant was that multiple ranks would be good, just follow the KISS principle (Keep It Simple, Stupid). I actually like the idea of having soldiers with the ability to 'level up' as they gain experience; just don't make it too confusing.