What is the counterplay to ranged undodgeable burst?
If your answer is nothing, you are correct.
I will give you an example:
When rengar wants to assassinate someone, his stealth is known to the enemy team, with an indicator over his closest enemy. He has to jump into melee range with very little durability, hope he does not get ccd or exhausted, unload his full combo perfectly, and even if he succeeds, he usuallt ends up dying.
Meanwhile twitch does the same thing, except with his stealth indicator being too close, having 850 range, so most champions can't even fight back, has the same burst potential, does it to the entire team instead of one person, and lifesteals while doing it.
How is this remotely fair?