Why bother with mundane classes if they're strictly inferior? The point is that balance is necessary, and that if there's any desire for V-tude, limiting how good non-magical player options can be, the workable solution is to tune magical options to balance with them. That they could as easily be intentionally imbalanced low to make playing a caster a woeful sacrifice, is just making the point.
More philosophically, even the most trivial magic could mean something in a given setting, or have a very specific use woven into a plot. If, IRL, you could prove that you could levitate match sticks, you would be an international celebrity and drive physicists crazy.
Benders are clearly powerful individuals who can do impressive things impossible for non-benders.
There are still extremely important non-bending characters throughout AtLA. Sokka, Ty Lee, Mai, Suki, Piandao, the Mechanist, etc. Characters who have special (but perfectly mundane
in-setting) skills, training, resources. And in a world where spirits are very real and the supernatural is but a breath away, even mundane acts can have effects beyond what is possible IRL. And yes, there is a TTRPG for AtLA, so this isn't
just a narrative to game comparison.
Hence, this whole thing becomes rather circular. Verisimilitude requires limiting certain things and being completely hands-off with others, but the decision about what to be hands-off with is either totally capricious and arbitrary, or knowingly and intentionally biased. The "veri-" to which there is "similitude" is a
choice, not a
requirement.
Folks who like the things volunteered to get the short end of the stick aren't exactly keen on that. Being told, "oh, but you see, giving those things short shrift is actually
necessary for the good of the game!" when we can clearly see that it is simply a choice, in support of a very specific and narrow set of preferences.
"Verisimilitude" is simply a more subtle, wily version of "realistic." As soon as you start pushing on the specifics, its true colors are revealed: only
sanctioned breaks from reality are permitted, and all other things must conform, not simply to IRL physics (which are quite a bit more flexible than many realize...), but to the rather stunted subset thereof which is held in popular opinion ("pop physics"?) as physically real and consistent. Actual physical feats real Olympic gymnasts, archers, and swimmers achieve are usually impossible or effectively so under this stunted subset of our physical reality, to say nothing of mundane-but-epic feats fantastical characters should have within reach.
I very much appreciate that folks want to feel that a world is grounded, sensible, predictable. A place explored less through map and word, and more through action and consequence. That is why I included "Groundedness & Simulation" as one of the four game-(design-)purposes" in my possibly-incomplete taxonomy. But I find "verisimilitude" goes quite far past "I want a world that is grounded, sensible, and predictable." Coupled with various rather pointed preferences and the advocacy for certain design trends (which, notably, were
not true of classic editions; loot in early editions
specifically favored Fighter characters over other classes!), it amounts to a shell game of the problems of "realism." Advocates have recognized that "realism" is a problematic term, so many of them have cordoned off the problematic parts and just don't speak them out loud...until pressed.
You can have a world that is fully self-consistent,
and where explicitly-flagged "magic" is not the only way to exceed the bounds of what should be physically possible. The supernatural and transmundane are vast. They contain multitudes.
