I wouldn't say your poll includes everyone. There's plenty of roles that aren't in there - neutral objective control, split pushers, seigers, melee carries, cc tanks, damage tanks, sustain supports, cc supports, etc. And not all 'Secretive' roles are assassins (think - Evelyn. She's noted as an assassin but is more of a flanking tank) or Rek'sai (gotta be stealthy to get that flash -> unburrow off.
Personally, I'd say:

Powerful early game, powerful sustain, powerful 1v1 potential, decent split pushing, powerful in a teamfight if left unchecked (he's pretty much a melee carry, though most people treat him as a tank. Can jungle and top well, strong and satisfying ganks with a Q hit. He fights frenzied, meaning you basically just right click on your target, dodge stuff if you can, and go to town. Also super satisfying when you're tanking a Mundo with ur regen while the rest of team kills him. if he catches someone out, he probably annihilates them. Can take down carries 1v1 even when behind.

Don't you love that sweet one-shot? That Q onto an enemy who walked just a little too far away from their friends, and chaining those kills together? Leaping over their heads while taking down the weakened targets? Yeah, Kha' is one of my favorites.

Tons of mobility, with E+Q and ult. Rushing a Rav gives you unparalleled kill potential with your E+Q+Auto+Ult+Auto+Rav combo. Corrupting potion first buy and E+Q the moment you get lvl 2, minions not required (though if you can get them, very useful!) almost always pick up a kill/force enemy back to base with that.
And finally, E+Q'ing through the enemy's entire team to one-shot their ADC/melee carry/mage and then running away frantically, burning flash to get out of your Cataclysm.
Also pretty high AD Ratios and built in Armor reduction.