Let's split that 20 year period up into four segments and address the key factors at play in each one:
- 1792-1799 (Approximately Valmy through Napoleon becoming First Consul)
- 1800-1802 (Approximately Heliopolis through Peace of Amiens)
- 1803-1809 (Camp at Boulogne and Peak: Ulm through Wagram)
- 1809-1814 (slow, then increasingly faster, decline)
Valmy through First Consul:
The French are winning consistently through this period, but they are doing so by virtue of significantly out-numbering their opponents. Valmy was 52,000 vs 34,000; Fleurus was 75,000 vs 52,000; Diersham was 60,000 vs 17,000. Most of these are really tactical draws of about equal casualties, but strategic victories for the French because they have threatened the opponent's LOC and not been beaten off.
The strict meritocracy of the Terror and Directory (win or meet Mme. Guillotine) is training a generation of French commanders with more experience under fire than Frederick a generation earlier attained in a lifetime. The French conscripts of the early Revolution are acquiring a habit, and a taste, for victory, and passing their tribal knowledge on to each new year's recruits. Only a rising star named Buonaparte is developing a reputation of being able to defeat larger (albeit Austrian) armies.
Heliopolis through Peace of Amiens;
The French start to show tactical superiority, with commanders other than Bonaparte winning when outnumbered, such as Victor at Montebello and Moreau at Hockstadt.
Berthier, as Napoleon's personal Chief of Staff, is building a rudimentary staff organization that will later inspire Clausewitz and von Moltke Sr., and will translate Napoleon's energy and vision into written orders that mere mortals can understand and accomplish.
Camp at Boulogne:
This long interlude enables the Army of the Revolution to become the Grande Armee of Napoleon. Ney publishes Military Studies; Friant, Morand, and Gudin train their divisions in large scale skirimisher maneuvres in broken terrain, as part of Davout's III Corps. The force that emerges to initiate the Ulm and Austerlitz campaigns is far and away the best trained, as well as the best led, army on the continent. This army is the instrument that Napoleon wields like a scalpel against Austria in 1805 and 1809; that humbles Prussia in 1806; that exhausts Russia in 1807; and that chases Moore out of Spain in 1808. This is the Old Guard that, in skirmish order at 100 yards over about 60 minutes, forces two batteries of Austrian 12 pounders to retire at Aspern-Essling, as well as Larrey's flying ambulance that returns an astounding percentage of the Old Guard wounded to their units in time for Wagram.
The guerilla war* in Spain and Portugal would bleed this army dry, and the calamitous 1812 campaign dismembered most of the rest of it. Napoleon needed another peace, and the Spanish campaign ensured he never got it.
Name the truly exceptional commanders on the Coalition Side, capable of brilliance in a completely independent command: Wellington; Nelson; likely Suvarov; and maybe Kutosov;
Name the truly exceptional commanders on the French Side, capable of brilliance in a completely independent command: Napoleon, Desaix, Lannes, Davout, Massena, and maybe Soult and Kleber.
At the next level down you have numerous competent, but slightly flawed, commanders available on the Colaition side: Blucher, Hill, Radetsky, Charles, Wrede, likely a dozen or so others
On the French side, many more: Kellerman (Sr. & Jr.), Friant, Morand, Gudin, St. Hilaire, Grouchy, D'Erlon, Victor, Murat, Eugene, Gerard, Vandamme, and many many more. Nearly every General de Division can be argued for on this list, and many of the General de Brigade.
Morale is always vital in warfare, and few events inspire morale better than seeing one's wounded comrades returning to the line. Consider the 1200 or so Guard casualties at Aspern Essling (from Bowden & Talbot, Armies on the Danube 1809):
Returned to Active Duty 600
Returned to France 354 (including amputees)
Let's think on these numbers for a minute. Two 12-pounder batteries, 12 guns total, firing canister at 100 yards say twice a minute, for an hour, fired a total of roughly 1,440 canister rounds in that time. All that shot inflicted less than one casualty per canister round fired, and barely 0.1 death per canister round fired. That's how good French skirmishers (granted, the Old Guard) were at avoiding fire! After an hour of this, the Austrian artillery retired due to excessive casualties, allowing the successful retreat of French forces back to Lobau Island.