Isn't Exhaust Unbalanced?

I used to main akali, but now, I feel like I do nothing. Every time I pick akali, enemy mid just takes exhaust, and with it's quite low cd, pretty much everytime I try to do a committed fight, it's up. This goes for assassins in general who have to dive into the enemy team to get their kills, unlike adcs. Which is why exhaust on ADC's etc is okay, who have their tank peel and kiting ability. but I feel like on assassins, it makes the assassins contribute nothing, who are forced to dive in for kills but with exhaust slow and 40% damage reduc..