How? o.o
Riven is actually one of the champ that can out duel Zed. Of course you still need to dodge (riven is very good at juking), but if you time your spell right, you will lock him down completely. Your E is pretty good against Zed, I can't remember exactly how much CDR, but you can E when he go in and it would be off cool down for you to shield again for the time bomb damage.
Why are you complaining about Riven anyway? She was the bane of top lane. Just because the meta doesn't favor her, you immediately want people to nerf other champs to the ground. This is exactly what people feels like when Riven dominate top, but they all hate 1 champion, not like you naming half of the top lane roaster.
Why don't you just wait, not a long time ago, people use to trash talk about Lux suck and being a useless pick... look at her now. Morgana was made fun of in season 3 for not being able to fill either support or mid... look at her now. Shyvana use to be one of the worst pick for jungle, due to no CC pre 6, and even then she got several moment last year when she was FOTM.
If you truly love a champion, then you can wait. If you can't wait, it mean you do not like the champion design and would rather play something that can win the game. If you want to be one of them, then go ahead, play Fiora