I know, you're right.
It's my opinion the main problem is how EASY the 100-0 comes. Too often it comes from point and click, or -guaranteed- setup. I think delayed burst on a class whose only purpose is removing a key player from the enemy team is poor, full stop. It's like suggesting every tank HAS to wait 2s for their defensive steroids to activate.
I think Talon's assassinations are comparatively healthy. His kill condition is his bleed, which you CAN trigger almost instantly, but because it is a DoT it is ALSO possible for you to be shielded or healed to survival, but by then Talon did his job, so to speak. Contrast to LB, whose assassination actually literally requires she wait to even trigger it and it can be denied by actually just walking away unless she used her E, but then she has to aim and hit you AND still wait for her main damage tool to proc? I think this would be much healthier if she didn't need to wait to proc her sigil, but her sigil explosion itself would be delayed, but LB would get in and get out. From there, the target dies if alone without healing or shielding or if not, their support saves them, as they are intended to. Why not give LB passive a Living Bomb (WoW) type of mechanic where her Q marks her target and if the target is hit with another spell (conditional) then the sigil pops, erupting for a certain amount of damage after 1s. Maybe her ult Q becomes a skillshot nuke that deals more damage than it currently does but it requires aiming, so you can't just QRQ to nuke someone point and click.
I appreciate the whole "don't wanna step on other character niches" but i don't know how many healthy ways to implement assassinations that don't feel bad to execute exist that are ALSO unique and fresh, to be blunt.
I don't think you should have TIME to REACT to an assassin. That's -literally- the point of an assassin. I 100% think ALL assassin burst should be avoidable to some extent that is not solely range. If your counterplay is don't be in 700 units of me if i am on my power curve (Akali.....), you are a poorly balanced assassin.
Kat is a perfect example too. She does wayyy too much damage with electrocute rn, but you are not killing shit as Kat with only her targetted Q and E, point and click or not, because her burst is tied to her daggers. Conditional. You CAN avoid the bulk of her intended burst, just right now Electrocute and the preseason are out of control.