I know you are right. And I know all this, but at the same time it is as helpful as saying somebody who just died -> Don't die.
If someone should go all in on you, stay close to your team to punish the engager.
If engaged on me, I am already dead
If engeged on somebody else, we punish but if his/her team follows the same as in every timefight happens, either your team protects you (rare when they spend everything on punishing) or they engage while the other team does the same and go for you, the squishy. SO you run again
Otherwise try to poke as much as you can with correct positioning.
Until you get caught and this is not an exagertation, there are many champs against which you can not poke as an ADC you will get oneshot if you step in range, and your ranke is the same or shorter than their engage range most of the time. What protects you is your team and their fear to just trade kills. They want to win, not trade.
As long as you stay behind your team and hit what's in range,
This is impossible. Either my team takes freedmg (so i am in range to harras) or they stay out of range (what makes me unable to poke)
Again I know you are right. And in essence I agree, but this is how it feels right now to me.
And I had plenty games where it just was no option to be anywhere close to the fight and it actually won us the fight that I wasn't there and chars like Jax held their spells in anticipation of me joinging in and just used them when it was to late for them since I never joined the fight.