[{quoted}](name=Crescent Dusk,realm=NA,application-id=3ErqAdtq,discussion-id=T8fXzkXh,comment-id=001b0001000000000000,timestamp=2019-07-06T15:27:22.490+0000)
Untargetable means jackshit when all it takes is one CC to blow you up and all of them besides Ekko (who doesn't have the burst of most assassins) rely on ult to get a kill, which is negated by later usage of PD+GA and support shields. You also say free flash every 3 seconds, well that is late game and it currently takes less than 3 seconds for an assassin to be blown up in late game. A draven or jinx late game with just 2 autos is stripping off 2/3 of your health as an assassin.
You laughably say that these assassins have an escape if they don't use their engage. Well, guess what, Rengar ain't killing shit without his ult and Talon isn't proccing passive without his ult either since only vegetables get hit by his return rake with all its delay and the fact Talon's single engagement tool is a short range 575 linear leap that means it's easily foiled by linear CC since opponents will always know where he lands.
Doesn't matter Fizz is untargetable with his pole, because he fucking needs to use it to land his damage rotation, by the time its cooldown is back he's dead in a teamfight.
There is a reason LCS doesn't use assassins besides Akali. Assassins suck ass the moment you have a single tank jungler or support in the team comp since you just get immediately peeled in teamfights and both bruisers and ADC's outscale you. This makes an assassin pointless because a late game Jax or Irelia or Renekton or Aatrox assassinates a backline way better while being far more survivable than any assassin.
Untargetable gives your team time to move in and help. If they wait for you to be targetable while teammates slaughter them, then they gona end up quite badly. As told you are NOT MEANT to go into 1v5, and kill someone, then escape. Though some assassin can do exactly that, if enemy got 0 defense, and no protective support.
As for engaging with Ult. The only one who got problem with that is Rengar. Talon can still escape without it, if there is a wall nearby. Chose your fight man. Don't just rush in alone against the group in the middle of mid. Eve uses ult as final attack, or escape. Ekko has very difficult time trying to engage ulti. Also doesn't make sense, because that would waste the healing part. The others have very low ult. CD, multiple charges, or ult reset on kill.
Though playing like you imagine is not impossible with some of them. Zed, Leblanc, Eve can do such. Go in, kill target, or make sure it uses emergency stuff in less, than a second, then escape. Repeat the moment ult ready, and enemy won't have emergency stuff that time.