Imagine a world like any standard RPG games. In these games characters grow stronger as they defeat opponents, long after any real-world soldier would have reached their peak possible performance. In these RPGs your level 100 PC is practically a 1 man army taking on dozens of foes at once with little risk; while in the real world even your most elite solder is only human, he can still be taken down by a few simple infantry men teaming up against them, or even die to a novice due to bad luck or one bad mistake.
I want to imagine a world closer to the RPG ideal, not just for PCs but for everyone; and people in this world are aware of it. People never reach quite the level of one-man-army as allowed in some RPGs, and it's more complex and variable then kill x foes and your certain to gain a level, but It's a known fact in the world that experience or training can let someone reach levels of Charles Atlas Superpower that make them able to greatly surpass the strength of a person with basic training alone. Most will not, or could not, reach the upper echelon of power, as factors such as innate talent, severity of training etc affect how fast one will grow in power and some simply will not have the raw talent or dedication to raise to the top levels of strength. Generally as one gets better raw training alone does less, and often combat experience against real threats becomes the main way to continue to grow powerful.
Now imagine a military in this world that acknowledges and expects this level of variance in power and skill. The military has soldiers that span the spectrum of power, but of course there are more of the inexperienced weak then the elite solders. Effectively you have a pyramid of lots of new fighters, decent number of competent, some veterans, and tiny number of elites. The power of the most elite solders are quite powerful, able to take on large numbers of rookies, but they are not invincible, bad luck or mistakes can let less skilled foes beat them and numbers and team tactics can easily allow a number of skilled-but-not-elite solders to defeat a more elite one. The military's power is mostly dependent on it's large number of less experienced common solders, simply due to the vast number of them compared to the more powerful, but the power of more veteran and elite soldiers is highly valued and recognized as an important factor in battles.
I'm trying to figure out how militaries would adjust by recognizing and utilizing this power potential. How would the relative skill level of soldiers decide how they're assigned, how does one use veteran or elite solders, more powerful but increasingly less common, to best utilize their power to support their less skilled solders etc.
What about rookie solders, how does one deploy them to make the most of their numbers while recognizing that there may be soldiers of noticeably higher strength they are best not used against out there on a battlefield?
For that matter if there is an expectation that generally speaking soldiers will manage to keep growing more powerful with experience (though this is general, and significant variance on how quickly one grows in strength and maximum potential) affect how soldiers are trained or utilized? Will there be a higher focus on keeping the rookies alive long enough to get some skill under their belt?
I'm looking at your average fantasy pseudo-medieval world in terms of technology. This also means smaller military sizes of standard medieval worlds.
You can also presume some level of unorganized non-sentient monsters in parts of the world, with the military being responsible for driving back monsters which wander to close to civilized areas, meaning some degree of constant threat even outside of war, but with monsters being weak enough that the military can hold them at bay; a soldier can die to monsters as part of the hazard of combat, but no one expects monsters to actually wipe out an entire patrol...