I gotta tell you, the bottom line here is I really don't think anybody at Riot's balance team has a freakin' clue about what an assassin is supposed to do.
Assassins exist for one reason: Kill. They go in, kill, and leave. Rinse and repeat. They are not scored by assists and farm, the goal is to target carries and execute them 1vs1 via ambush. That's the whole point of what you do when you play an assassin is to kill the person quickly or get punished for screwing up. Yet, Riot bases most of its formula on assassin's on farm and assists, which is not the goal of the class at all, to get the much vaunted S rating. I understand it is a team game but assassins are supposed to be the ones taking kills over assists much like ADC's.
I don't think Riot learned a damn thing. Camille is a great example of a champion who was repeatedly nerfed because of perceived strength - every champion has either a higher or lower than usual winrate for the first month. Rather than wait two months to see how the original nerf went, they nerfed Camille -seven- times in the course of three patches. Suffice to say, I rarely see her anymore. So Camille's ult vanishes when she dies, but Heimerdinger's turrets keep firing for 4 seconds? Morde's R still exists until the duration is finished? These things make no sense for an ult that itself does no damage and punishes divers, lasting for four seconds. But, hey, as long as we can dash around the rift throwing tornadoes every 1.3 seconds and block anything coming our way with a giant indestructible wall who cares?
The LCS is the major issue - Riot wants people to be like the pros, quite obviously. The best way to do that is with Team Builder returning - guarantees you your role and champion of choice. They removed that so now blind picks is just fighting over roles. The pros have a specific person for a specific role - do you ask Faker to go support? How about asking Peanut to mid? Pros have their role -guaranteed- but Riot only gives a 50% chance of your declared primary role in draft picks. Team Builder fixed this crap for three years and then they took it out and its been hell playing the game ever since, but it still beats waiting 5-6 minutes to find a draft game, going through 5 minutes of picks and bans, and someone dodging to repeat it all over again.
So with this mentality we have assassins who work more to farm and get assists than actually kill, people who are told to be like the pros forced to do roles they aren't good at when the pros have a guaranteed role because of their skill at it, items that are broken on arrival getting nerfed and new champions either buffed or nerfed excessively in consecutive patches.