Really dude? How long have you played this game? Assassins are meant to be single target, and let's look at the evidence of all of the assassins to prove my point so buckle up cowboy.
First, Assassins are put in solo lanes, specifically mid the center point of the map
Zed: Q a single target shuriken that does more damage on the first enemy hit
Zed: W designed to get out some poker with his Q and slow with his E making it easier to catch up to people, also fucntions as a dash to get into the backline to kill the adc
Zed E: a short ranged AOE slash that has its cd reduced every person it hits, Also slows when cast by the shadow
Zed R: A point and click single target ability that does more damage to the person the more abilities they get hit by and the more damage they take
Next up talon
Passive: A 3 hit mark on one person
Q: a single target dash that causes the enemy to bleed
W: A slow that can give 2 stacks on his [passive if both hit, landing a lot of damage
E: A roaming ability and escape ability, this can be used to go to lanes quicker, go to bot lane and get 1/2 kills
R: GOES INVISIBLE and gains movement speed, then decided to run at the backline because he can
Next up Akali
Passive: Legit more damage on an auto attack
Q: A very short cone blast ability that heals
W: TRUE STEALTH, that allows her to dive towers easily and get away from situations
E: A dash that follows you through any terrain, also single target ability
R: 2 dashes, one of which slows, and the other is an execute
Next Ekko
Passive: A 3 hit passive onto someone that gives him movement speed
Q: Like talons W except worse, if landed correctly gives you 2 passive stacks
W: and AOE stun, that if caught out will ruin your life, can also be good for escaping ganks
E: A single target Dash that does damage
R: A button to fix your mistakes
Yasuo
Passive: Sheild
Q: a(pretty much) single target slash, and a knockup
W: blocks all projectiles
E: Single target dash
R: Screws over a person he sees and also gives him bonus damage on his AA's for the next 10 seconds
KhaZix
P: Punishes you for being alone
Q: single target slash that can be upgraded into a better single target slash
W: A skill shot that can heal him and slows enemies(can be upgraded to hit more enemies and give a better heal)
E: A leap that goes farther than my father(can be upgraded to let him leap again if he kills someone)
R: Invisibility
Rengar
P: legit allows him to give the enemy a heart attack
Q: single target strike
W: Cleanse/restores health/ tiny AOE Ap scaling kitty roar
E: Single target slow/root
R: Do I even need to explain this one
Kayn:
Q: a slash
W: a slow/knockup
E: allows him to go through walls
R: OH YES DADDY(he dashes and becomes in alpha for a few seconds)
Kassadin:
Q: Gives him a shield
W: bonus attack on the next ability
E: A slow
R: A blink every 2 seconds
Fizz:
Q: single target dash
W: Rends an enemy
E: A giant "fuck you" to the enemy
R: throws out a fish to one person to where a massive shark spawns
Everlynn:
If you can't tell that this person is all about killing one person you need to check up
Nocturn:
Q: Single target darkness and that leaves a trail that gives him extra movement speed
W: Spell shield
E: Fears a single enemy
R: A single target dash that also gives the enemy a seizure
Pyke:
Q: A single target hook
W: An invis ability to help get into the back line potentially
E: A dash that also stuns
R: An execute ability
Ok so now tell me that assassins based on their abilites, all dont have a dash to engage/ get away, a ton of single traget abilites and some sort of unique ability to them. Youve lost this case dude, you're being downvoted. Admit you're wrong an lets move on.