Both supports and ADC's are part of the issue.
I cringe so much when people post threads that get popular with something a long the lines of "It's not the supports, its ADC that are OP" or vice versa.
Look, I understand you really want to prove a point, and I agree with some of it, but single handedly defending one side is stupid by blaming the other.
ADCs and supports are a symbiotic relationship, Currently the most powerful supports are the ones who can really protect a Hyper carry(or a regular carry, but for the sake of the point) becuase Hyper carry Items(Crit) got some buffs making their overall contribution, when uninterrupted, very large. Tristana/Janna are the current perpetrators of the ultimate symbiosis, be it multiple factors why. Energized got more powerful, incentivizing more crit in trading off sustain when BotRK was the hottest shit around. Hence forth, having heavy crit means low sustain, so supports who can provide that sustain or pseudo sustain(peeling/negating damage) are more highly valued. But when BotRK was meta, Supports were largely more aggressive because of the sustain and dueling power that BotRK provided.
My point being, The ADC is kind of a big deal, but supports are not totally innocent either. Reducing supports Sustain/mitigation makes it more risky to play a crit heavy ADC. Reducing crits damage make it less rewarding for ADC's to opt for the route. I'm not an expert, I just main Tristana and I totally understanding the general consensus towards her being a extremely safe, and powerful, ADC despite how clunky she can be. She wasn't powerful before because people were playing aggressive supports with semi aggressive ADC's, being Cait, Draven, Twitch and the like. The second people started realizing that playing a safe support instead of the more risky and aggressive ones that can easily throw lanes with a single misstep, boom. Safe supports can keep their carry in the game, going EVEN with hyper carries is winning, hence pick a strong carry and go even, if not winning lane jungle presence provided. This protecting the ADC meta is a bit anti fun for two reasons. It makes it really hard for anyone to shut down an ahead carry(god forbid it's a hyper carry) and even if you beat them down, they will eventually come back up, unless you apply a constant pressure team wide on bot lane, which is a chore and a risk. Safe should not be the end all, be all. Aggressive(Bork) and poke(Lethality) play styles need to be supported too.