Should Riven's ulti be given a longer cooldown

So I was in a game, I was Jayce vs Riven, and I knew I had a chance to beat her when her ulti was on cooldown but by the time i got done with the poking my mana is low. She used her ulti I got out, I recalled and tp back, I go tp back she uses her Ulti once more. I mean this is not really fair as she has good health regain now, a nice escape and a good sustain in lane. So I have to worry about my shots because they need to hit otherwise my mana was wasted for no reason, if Riven ever misses something its okay, she can do good damage against me, I got back, maybe this time I dont have TP I have to buy items then run back to lane and by the time the poking starts again her ulti is up. Now I did manage to kill her twice, once under my tower and second in river, but thats only because she forgot to Q me, so what do you guys think about Riven's ulti, should there be a longer cooldown?