The discussion of rank here reminds me of a passage in H.H Krist's "Revolt of Gunner Asch". In this the Lieutenant reflects that he doesn't need to command 134 men himself, since the army works by groups of 6-10 men. He has half a dozen senior NCOs that he deals with; each of them is responsible for a handful of junior NCOs, and each of the junior NCOs is responsible for a squad or gun crew. Since its foundation the US army has doubled and possibly tripled the number of Enlisted rank levels that it has. For a full history, see here. This is further complicated by at least four grades of warrant officer, which unlike in most armies are not a form of Sergeant Major. It's been claimed that a sergeant in the US army is only the equivalent of a Lance-Corporal in the British army, partially because of the system explained here.
By contrast, the British army has got by with a smaller number of ranks for at least 400years.
At the moment I'm reading about the Tugars –a very organized nomad people on the asian steppes. Their ranking system was "leader of ten" (a squad), "leader of a hundred" (squadron), "leader of a thousand" (battalion),"leader of ten thousand" (division) and commander in chief (Emperor). For the sort of warfare they waged (raiding or mass-attack) this was ideal.
Here is a possible model for a new, simpler system:- Non-officer ranks are designated S-n, though unlike Mike Sparks' system, this stands for "Serviceman" not "Soldier". Soldier actually means Serviceman, but I'm changing the term since this system could also be used by the airforce.
S1 Private, Gunner, Trooper, Sapper.
S2 Lance-corporal, Private First Class, Bombadier, Senior Trooper. Team Leader or Assistant Team Leader.
S3 Specialist or Technician. Has no field command authority except possibly in his field of expertise. Rank for Aidmen and RATELOs.
S4 Corporal. Team leader or vehicle commander.
S5 Sergeant. Squad Leader.
S6 When 2 in C of a platoon, "Platoon Sergeant". Otherwise, Staff Sergeant, Colour Sergeant, Senior Sergeant.
S7 WO2. Warrant Officer. When senior non-officer in a company, "Company Sergeant Major" or "First Sergeant". The American term avoids confusion over Squadrons, cavalry troops etc. Responsible for the day to day co-ordination of the Platoon Sergeants. Other WO2 titles would be Master Sergeant, Company/Squadron Quartermaster and Flight or Pilot Sergeant. A S7 in command of a weapons platoon is refered to as a "Platoon Master Sergeant.
S8 WO1. Chief Warrant Officer. Highest non-officer rank. The senior WO1 in an unit is called the Regimental Sergeant Major (or maybe just Sergeant Major). There will usually be only one of these, regardless of if the unit has one battalion or half a dozen. The RSM is responsible for the day to day co-ordination of the CSMs/ WO2s. Other WO1 positions are Quartermaster Sergeant, Pipe-Major, Drum-Major, Conductor and Senior Flight Sergeant.
Officer Ranks, as before.
There may be a case for having both PFC and Lance-corporal/Bombadier ranks;- in other words, having a grade of senior private. In such a case the Lance corporal rank shares S3 level and has the responsibility of Team Leader or Assistant Team Leader. This rank structure gives a very simple and effective system.
Squads are lead by Sergeants, assisted by Corporals and Lance-Corporals.
The platoon is lead by a Lieutenant with a Platoon Sergeant as second in command.
The company is lead by a Captain with a lieutenant as EO and a First Sergeant.
The Battalion is lead by a Major or Lt. Colonel with an EO and a Sergeant Major.
