If you don’t think that controlling where load is carried on the suspension effects your traction, your high school physics teacher failed you miserably.
You say you’re not adding traction, well, that’s a silly way to look at it. By that definition only tire compound will ever add to your traction. All any suspension is ever doing is keeping you from losing traction. So just run without it, it’s not adding traction by your logic.
And why do you need to improve an understeering car with a stiffer sway bar? That doesn’t say anything about what a sway bar does. Sure, you can be in understeer if you’re already too stiff in the front, and adding front sway bar won’t help that. But that doesn’t mean a sway bar can’t improve traction, it just means they’re not always the solution to a particular problem. Of course, you could be in understeer because your front suspension is too soft and you’re bottoming it out on braking and entry, in which case adding wheel rate might actually help. You’re vastly oversimplifying, and your own “camber issue” example shows that. There’s a lot of possibility’s that you’re just flat out ignoring.
As far as improveming lap times, improving traction is the number one way to do that. If driver confidence is a bigger factor then it’s inexperienced drivers that’s the problem. Which is exactly what you see in Miata racing, because that’s entry level competition. So yeah, maybe a bunch of inexperienced drivers like you’re used to seeing just use sway bars as their magic feather, because they don’t have a clue what’s actually going on. Might not want to use them as your example.