They were changed so that an assassin couldn’t jump into the middle of the team and kill the squishy standing next to the support and tank, and usually getting away with it.
Now the problem is that then peel and shield/heal supports got buffed up, which made the damage delay a lot more of a burden, and the assassin’s damage much less potent.
Assassins still need a form of counterplay to them, they had much too high of a reward nearly always guaranteed. But peel/shield comps also need to be toned down so that assassins can actually do their job.
(Also, assassin players need to stop complaining when they try to kill a fed carry when they themselves are behind, and subsequently failing. That’s more on you being behind, not assassins being weak.)