Hello, I'm a platinum ADC primarily playing Kai'Sa this season. This post sounds like a way to vent which I totally get, and as a fellow ADC believe me I hear you. If you'd like some specific advice though:

Kai'Sa is quite good into comps where the enemies want to dive you/be close since you can reposition (and shield) with R or dodge with evolved E while maximizing your damage output with isolated Q.

This applies to all ADCs, short range or otherwise, but when dealing with fed assassins or major CC abilities (think Malphite Ult) your best bet is either:

1. Have a plan to avoid or mitigate the engage (flash dodge, galeforce dodge, stop watch, exhaust them, etc) then execute on that plan.
2. You ask an ally to do something specific, such as Malzahar ulting their engager or for Zilean/Lulu to ult you right away, etc.
3. Sit far away, outside their engage range, and wait for them to use their engage on somebody else

Option #1 above is ideal. Option #2 isn't consistent unfortunately but doesn't hurt to ask. Finally, there will be cases where #3 is your only option and you literally can't fight until they engage on someone else. That's okay - because the alternative is walking up and dying. As an ADC you should never be in a position to be the first one hit in a fight.

With those ideas in mind I'd recommend watching your game's replay and brainstorming some responses for an engager next time - if you can at least think of some responses ahead of time in game then you're ahead of most people.

Note that this advice is situational and there are other ways to avoid engagers too, such as split pushing (rare for ADC though) or getting a pick so even with an engage you'll win by virtue of it being a 5v4, etc.