Riot seems to love AP assassins a lot more than AD assassins for some reason.

Let's take a look at 3 AP assassins:

And we'll look at 3 AD assassins:

Now my complains aren't gonna only be "Ohh the enemy just needs to build a ninja tabi to make AD assassins useless!" because the damage isn't the problem for the most part. The problem is the AP champs have more versatile kits that are just more powerful overall.

Let's compare... AD/AP

Decent dashes- AP wins because all 3 have pretty good ranged dashes, and Fizz's, which is tied with Talon's in range, can be made so much better with his E so he doesn't take damage for dashing into an enemy, and Rengar relies on bushes for his. The 3 AP only need a champ/minion.

Invulnerability- AP wins because both sides have 1 invulnerability (if you don't count Akali's which almost is one) which are Fizz and Zed. The difference is Fizz's has a lot more potential because it's on a much lower cooldown, he can control where he ends up, and it has the potential to be longer.

Roams- This is one where AD wins, but not by a lot. Talon and Rengar both have good roaming power, with their E/R respectively, but Zed has about asm much roaming power as the AP's. The difference is when they get to the lane they're roaming to, the AP's can use their generally better dashes to close the gap and make the gank successful more easily, something that Talon especially cannot do.

Snowball- AP's, 100%. I mentioned this isn't only gonna be a ninja tabi OP thread but it deserves to be mentioned. People building armor against the AD's feels so much worse than building MR against the AP's. Zed and Talon's win rates fall off a cliff around the 30-35 minute marks according to champion.gg because when people stack armor you can do nothing. Fizz and Akali's win rates have a small dip towards the end of the game, but nothing like the AD's. This may be because AP has Mejai's and AD has nothing like that to help them snowball.

These are the 4 categories that I feel make a good assassin, and how the AD assassins compare to the AP assassins in my opinion.

TL;DR: AP assassins are generally much better at being assassins then AD assassins, and the AD's need some love.