An Enemy Spy Reads The Wheel of Time III: Something's Fishy in the White Tower

[Malak'ai]

No, it is because they all have those powers. Lan is canonically the greatest sword fighter alive, Perrin is a child of prophecy, and every single Aiel is depicted as being capable of fighting dozens of trained human soldiers. Including Borderlanders, whose society is at least as militaristic as the Aiel.

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And then there is them having more casters then the far larger population of Westros combined and a larger combined army despite living in the desert.

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The Seanchen are great because they have a professional army. Their soldiers don't get touted as being inherently more athletic and talented then others, they don't have way more people and casters then they demographically should, and they aren't a bunch of unstoppable tribesmen despite lacking organization.

The Seanchen win on using casters in tandem with their armies where everyone else trains them separately (including the Aiel, Aes Sedai and Ashaman) and using a menagerie of monsters that invalidate specific tactics (cat beasts that scare off horsemen, flying scout monsters, etc.)

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I think that you're forgetting that the Aiel population is mostly made up of warriors. Somewhere around 60-70% are full time combatants.
Twelve full tribes, if we're taking the Shaido as an example (including the Brotherless) is 1920000 people. If only 60% are combatants then that's still 1152000 warriors, so the demographics are about correct.