Ok, so you are a bad ADC. Vi's ult only does at max rank, about 7-800 damage, max. With the reduction from only 50 armor, this brings the total damage down to 550 or so damage, again at max rank and with the standard build. This means that at the same time, the ADC probably has 1500-2k hp, easy. So you are only losing 1/3 to 1/4 of your hp to her ultimate. At which point, you team turns on her because she is now in the middle of them and they pop her easily. If you are not good and have itemized poorly, and not know how to kite away/use flash/heal right, then yeah, Vi can kill you with a rotation. But here is the thing. Vi is a diver, that is what she is supposed to do. And even if she does kill the ADC, she is guaranteed dead if her team doesn't follow up perfectly, and even if they do, she is probably out of the fight. You ADC mains are so butthurt about not being able to absolutely destroy people anymore, you look for any excuse to be made overpowered again, and I am not having it. There is counterplay, you just have to be smart enough to use it. The counterplay to Syndra is to buy an MR item like edge of night or Maw, Malzahar is the same, or a QSS, and to Vi it is not to go alone. Are there any more champions you need me to explain for you? Maybe you dont know this, but you shouldn't go near an Annie with her stun up, or towerdive a Shen, either. There are champions/roles specifically designed to counter other champions/roles. It is a circle, and that is why teams are not picked blind in ranked.