Why playing with ADC is better for your elo?
Ranged > meele for carrying. As you take less damage for the ammount that you do EASIER and in more sophisticated way.
+ if you lane bot lane you are the one responsible for the ammount of feed or feeding enemy ADC/support do. If you dont feed them or take them out all together = Enemy team cant really siege that easy and collect free win anymore. While if you are top and you take out your top laner tank 0 10, but their bot lane is fed. They all will just stand in their fed ADC range and siege, and if you try to kill them, those 0 10 tanks still have same amount of CC to peel you off.
Fed tanks/bruisers/assasins/fighters , all of those can be dealt as ADC either solo, or with a support/ good items. ( lifesteal and minor defence/ good kiting/ flash etc ). You have more tools to waveclear and stall game, unlike from the top lane where if you try to waveclear you get all inned and die instantly LOL.
+ another mention is that, if they have fed assasins/tanks whatever. To kill your base and push you back from CS they have to all in you or catch you. Both of those can be avoided like I mentioned before. With meele champ you dont even have that as an option most of the time