AD carries aren't really being touched on League of Legends Patch 8.7 directly but some of the items they build and even items that are often built against them are being changed.
Guinsoo's Rageblade is getting the cost increased again meaning Varus will take a bit longer to hit his power spikes. This should slow down his early game impact and make it more difficult for him to snowball turrets so easily.
That being said, he still has a great laning phase and is one of the few ADCs that brings crowd control to the table, still making him a strong pick going forward.
Kai'Sa got some huge buffs last patch and won't be touched in Patch 8.7. She's really strong but is in a weird spot where her optimal build still hasn't been figured out. Once that happens she will likely be a contender for top ADC but for now she is just outside the top three.
Her burst damage is insane so try to pair her with an engage support such as Alistar, Leona or Rakan to blow up enemy carries before they can react.
Since Caitlyn is so strong at the moment Ashe is seeing a resurgence due to the fact she can actually go even or win lane against Caitlyn. With Tristana's early range being nerfed, Ashe has become the go to counter to Caitlyn and even provides excellent pick potential with Crystal Arrow making her a solid all around pick.
Xayah still does a heinous amount of damage and can smash the laning phase when paired with Rakan. The only reason she isn't the top ADC is because her lower range makes it riskier to siege turrets.
Her team fight on the other hand is still incredible since she can go untargetable with Featherstorm and then AoE root the enemy team with Bladecaller. The insane outplay above showcases just how strong the duo of Xayah and Rakan can be when in the right players' hands.
Caitlyn has the simple advantage of too much range in the early game. Its almost impossible for opponents to trade effectively with Caitlyn during the laning phase. This often results in a huge amount of pressure in the bot lane and typically an early turret since Caitlyn can auto attack a turret from pretty darn far away.
Despite that early game strength Caitlyn is also a late game terror, making her a tough opponent to defeat. She even has the Yordle Snap Trap ability and mobility from 90 Caliber Net to help with her siege. All of this together makes Caitlyn a very well rounded bot lane choice.