Rek'Sai champion spotlight

what they mean is "rexai is not a super tank, hes actually a hypertank so dont worry, you wont die"

Yeah, her champion spotlight is way wrong on that one xD

I don't know.

To me a hyper tank, would need to have built in mechanic that make them hyper scale with the tank items they purchase. Or even have other mechanics that make them even tankier.

Just about any defensive mechanic that scales with defensive stats. (HP, Armor, MR) Including may of the Juggernauts who have regeneration abilities that scale with max HP. Sion also is a good fit since he has the Infinant health stacking mechanic, were his shield also scales with max health.

Rek'sai relies only on the defenses that come from items. Relying more on the utility of her spells, rather than tanky boosts.

She's a fighter, build half offense and half defense. She isn't a tank, her only cc is the W.