Assassin comps are too strong in TFT
I coincidentally happened to build an assassin comp. Started with Zed, Kha'zix and Pyke, in that order. I believe I only lost one round after that.
I also managed to get both Kassadin and Cho'gath which gave me the Void buff, and this ensured that I would continue to win EVERY single match onwards. After that I got a little lucky, pulling all of the ninjas needed for the full ninja buff. In the end I had the full ninja + assassin buff.
Thankfully it isn't possible to get the Void buff in conjunction with the other two (unless you use spatula), but nevertheless the game was quite the stomp. It's not like my opponents were unlucky as some managed to get 4-5 3 star units with decent items on some carries. Additionally, I can't say for sure I was so lucky since the win streaks allowed me to stay healthy enough to be greedy for gold. Gold in which I could spend freely re-rolling after 50g.
Another thing to note is that ninjas have plenty of other passive trees to change tactics mid game if your current team isn't cutting it. The insane amount of versatility the ninja tree provides is also complimented by the unfair amount of gold you get by running assassins early game. Because of this I feel that the ninja tree is fine any shouldn't be nerfed due to assassins existing.
Maybe this could be excused if the comp didn't absolutely dominate the late game, but after getting 6 unique assassins, the buff alone can carry the game for the most part.
In conclusion, the assassin comp is too strong and definitely needs to be nerfed. The ninja tree only adds to the problem with their versatility but. unlike for assassins, trying to run 4 ninjas can be very risky if you're not already so far ahead. Some ways to fix this problem is to just gut the assassin tree by limiting the buff to it's 150% critical strike damage, and nerfing the critical strike chance across the board or for assassins exclusively. In exchange to this massive nerf, the assassin passive would only need 2 assassins as opposed to 3. This limits assassins to the pure early game units that they should be, and with a nerf to critical strike chance (for assassins only or across the board) makes assassins the high risk high reward units they should be. Additionally, I would make Zed more rare. He is too good with the single ninja passive plus the buff for assassins that comes afterward. Zed should be as rare as Rengar, and to compensate, add another unit to the game to take Zed's place, one that's not a ninja.