In my experience with wargames so far, there seems to be a predominant assumption that any given type of soldier inherits a specific set of attributes. The attributes are usually numbers, such as a target number to hit an enemy when attacking, or how many wounds a squad can endure, how far a squad can move during a turn, and so on. It seems that wargaming miniatures are often treated, by each game at least, almost like trading cards, with immutable attributes and traits. The effect is that, for example, you buy a Peasant miniature and get a 3 Strength weapon and 2 Armour, but you buy a Knight miniature for a 4 Strength weapon and 3 Armour. Obviously the miniatures themselves are not inherently more or less powerful than one another, and you could easily play in a mirror universe where all your Peasants are more powerful than your Knights. But that's not how most wargames treats miniatures, and there are advantages and disadvantages to that design.
Miniatures in most wargames are essentially monolithic. You get a miniature, and your game assigns it a set of attributes. You can't have a Peasant that got hold of a special weapon, or a good set of armour, and all Knights always have the best weapons and armour.
However, there are some wargames that exercise at least some modular design. The rules might provide you with special abilities or bonus gear or penalties that change a miniature's profile. You can have a Knight miniature with flimsy armour but the ability to move twice as fast as the others, and a Peasant with a powerful weapon that deals more damage than usual but tends to hit less often.
As with all design decisions, there's an associated cost with each design philosophy.
As demonstrated just by my simple example of a Peasant and a Knight miniature, miniatures may not have immutable numbers printed on them like playing cards do, but they do often suggest an in-game logic. A Knight is probably very obviously wearing mail or armour and wielding a finely crafted sword, while a Peasant likely carries a club or a shovel, and wears rags. It's immediately obvious which miniature ought to be more powerful, and after a few games it's a constant visual reinforcement of which set of numbers you need to load into brain during a set of actions.
Going against the obvious is by definition non-intuitive. However, not everything is as obvious as the comparison of a Peasant and a Knight. In a scifi game, there might be 10 different gun types, weapons and power weapons, flak and carapace and plasteel armours, and technical gadgets that scan or hack systems or conceal targets. Because miniatures are just toys with guns that don't actually do anything, the difference between gun types usually is defined by its visuals. The big gun gets a big name and does lots of damage, the little gun gets a simple name and does a little damage.
That's intuitive design, and it's well suited for plastic miniatures that aren't terribly modular once they've been built (unless you go to great pains to magnetise them so you can swap out weapons.)
To some degree, a plastic miniature provides its own design requirements. A sculpted miniature carrying a gun needs rules for a gun attack, and a miniature with grenades hanging off its belt needs rules for grenade attacks, and so on.
As true as that may be, the realism can end there. The same plastic rifle can reach 48" in one game but only 24" in another. It might fire piercing bullets in a historical game, but supercharged explosive rounds in an alternate history game, or even lasers in a weird scifi game.
Similarly, there could be several different armour options for a knight miniature. While building your army, you could choose a profile granting the knight very strong armour in exchange for low quality weapons, or the other way round.
Instead of considering a miniature as a playing piece with a singular definition, each element on a miniature can be "tagged" with a specification. Using a point-buy system, dice rolling (as in an RPG character build), or just a sliding scale of attribute collections, a game designer can grant static miniatures distinct ammo and weapon and movement values.
The advantage is that miniature definitions become flexible even within the same game system. How a game will play becomes harder to anticipate, and players gain many new possible strategies.
I use a custom build system for Middle-earth Battle Strategy Game, and I much prefer it to using standard profiles from books. Whether players roll dice to determine just how good a base value is, or whether you provide players with bonuses in exchange for build points, or you spec them out in balanced packages, introducing some variation in power is a great way to keep a game system fresh. Big battles and skirmishes can both benefit from modular miniature profiles.