I did state that I am entirely okay with it.
The dash is fine, because Riven's main shtick is being a mobile fighter instead of a particularly tanky individual. The shield lasts less than 2 seconds, so it's more for negating a burst of damage than any persisting combat DPS. The CD is a bit low, but aside from jumping on top of people for less-than-a-second CC, she has no other defensive tools in her kit. It only scales on Bonus AD rather than Total, and the base is low to compensate.
Besides, it's not like she's the only melee with a "Get out of now-you-fucked-up" card. Lee Sin has a dash with a shield, admittedly not AD-scaled, but it shields his allies and has a really long range. Fizz has a dash that pops and dodges projectiles. Yasuo can Wind Wall and walk away. Yi can usually avoid getting sniped via Meditate after running faster than Hecarim on speed.
It's not like Riven's the only champion to have an ability with unique scaling design. Shyvana's Burnout scales only on Bonus AD, but deals Magic damage. Ezreal's Mystic Shot scales on total AD as well as AP, but deals only Physical damage (and is basically treated as an auto attack).