tbh as soon as a squishy gets 1 item to increase their effective HP against Physical Damage, Riven's burst is fairly well nullified.
Take graves for example. If I know I'm going up against a Riven who is probably going to try to flash/dash onto my head, I'll run flat armor glyphs, scaling armor seals, and I'll buy something akin to the likes of Randuin's Omen that grants both Armor and HP. If they also have Magic damage burst (E.g. Kat or LB) I'll run banshee's instead of omen and end up with decent effective HP against both (as I have built MR + HP and I have innate Armor).