Riot completely destroyed her early and mid game itemizations, raised the cost of health pots (a universally bad move), and forced a meta so heavily reliant on oppressive right-clickers that Riven's one weakness (early game zoning) became her de facto death sentence.
You don't think there is a problem with the overall meta?
Riven's AD scaling shield should by all means be a monstrosity right now with the sheer amount of high AD fighter and bruiser items out there.
Yet she plummeted to 44% win rate in her only lane. Why? Because of how item dependent she is at all levels.
She lost her early game equalizer, she got gold-gated out of her only means of sustain, and her typical top lane match-ups got an item that delivers a 236% gold efficiency power-spike that synergerizes so well with two blatantly overpowered masteries that are pretty much useless for her. Made worse by rageblade also being completely useless on her.
Her only options in top lanes right now are incompetent opponents or build tanky and pray to survive; with the high cost of tank items and her complete lack of AP scaling means that a Riven that build tanky out the gate is a dead Riven.
But yes please state that a 0.4 per second buff is unfair or unbalancing.
Let's not even mention the 62% Attack Speed, 32 AP, 24 AD, 20 damage minimum magic damage on hit cleave that maxxes at 4 AAs, 2500 gold item that her lane opponents are using...