It doesn’t matter how fast the Riven’s hands are, the Riven player’s skill changes nothing in how you play against her. She can either stat check you or she doesn’t.
Contrast with all of the interactivity of fighting against a skilled Jhin. Be aware of minion HP, mind the trap placements, dodge or bodyblock his W+R, play around his bullets.
Against Irelia you watch your minions, keep an eye on her stacks, try to bait her W, dodge her E, and avoid being put in a bad spot for her R cage.
Is this bad design?
It is bad and outdated design, especially her basic abilities. R is kind of OK.
In the past there was no champions to fill the high-mechanics niche so she was left alone and now it is kind of too late because of her dedicated playerbase.