No, the one on your team who can blow up easier is the ADC, he's also (supposedly) has the highest amount of damage. So yeah you can protect the jungler who can dish out 3k damage on a teamfight, or you could protect the adc who can dish over 5k... take your pick.
Of course there are top laners or jungler carries who deal more dmg than an ADC, but you see, melee adcs have self peel, when you waste Janna's shield on a meditating Master yi that's not very optimal. Also, when the enemy jungler is able to SIMPLY WALK past everyone and get to your ADC you're definitely doing something wrong.
I'm not saying you shouldn't peel for someone else, but if someone goes dead straight to your ADC, ffs, peel him, that's not only true for supports or tanks, EVERYONE should peel that ADC, not because the ADC is important but because the enemy is OUT OF POSITION and getting him on a 1v5 will be SUPER easy, next step is winning a 4v5, simple as that.
I'd like to also mention that on a team, everyone has a purpose, if your ADC dies (even if it's his fault) he won't be able to do his job and it is of your best interest for everyone to fulfill their purpose, because when that happens, games are won, if the ADC has the chance to peel for a teammate he should also do it, it is of his best interest as well for everyone to fulfill their purpose.