Fiora killing a tank quickly and having a 2 second dash doesn't mean anything about her counterplay. There is probably more counterplay available to a tank vs Fiora than there is in any other 1v1 scenario this game has to offer.
Riposte is obviously designed to let her stop the plays you're making on her but there is a lot of gameplay around it - let's not forget it's the only untargetable spell in the game that makes the champion stand on the spot.
I play pretty much every class that gets countered hard by Fiora (my mains are all squishy, immobile, CC-reliant mages), but she is in no way lacking in counterplay. She has more than most champions.