A common misconception
A common misconception people seem to have (based on previous seasons) is that an adc is weak early game. That they need a support to take care of them through the early game and that they scaled better with items than with levels. While adcs do scale with items so does any champ really. The difference is an adc is a ranged auto attacker meaning a large part of their damage cannot be avoided. They may not burst as hard but over time their damage output was the best due to safety of range and the nature of autoing and the occasional crit.
However this season more than ever we see adcs in every role except for support. Their abilities scaling are good enough to get them through the early game ad stay on par with mages mid. More so their items give more stats then ever before. This was supposed to be balanced by lower ad amounts. However adcs have become tankier largely to burst damage (usually from magic damage dealers) and crit becoming more available they are criting more which is most likely making up for any loss in raw ad.
IMO the biggest offenders are
Youmuus: 65 ad, 10 cd , 20 armor pen, active that gives move speed and attack speed. Nice collection of stats. I think if adcs want this they should have a lower active duration (like it used to be) or only get the attack speed or movement speed instead of both.
Maw: 55 ad, 50 mr , 10 armor pen, 2 passives (why two?) one that stops magic damage from bursting you and the other that gives life steal and spell vamp to heal right back up and it last as long as you're in combat. This item i feel you should have the shield be an active so at least there's a chance that you misplay with it. Or remove the second passive. Third option instead of in combat change it to damaging champs so you can't destroy a minion wave and be healed while still maintaining the passive.
Essence Reaver: 65 ad, 20% crit, 10 cdr, 2 passives one that gives more cdr for building crit and the other that gives mana for criting. My question is why do they have to give up nothing to for all these stats? Before if you wanted cdr on an adc you had to go out of your way to build it at the cost of crit, damage, or lifesteal and you were often relying on a tear for mana delaying your damage. Now you build this and an ie and now you have most of the stats you would need to become manaless with a chunk of cdr.
Mericurial Scimitar: 75 ad, 35 mr, 10% life steal, 1 active that removes debuffs and speeds you up. Gives a lot of ad for a defensive item. It also has lifesteal tacked on because why not. I don't have a problem with the active but maybe limit the speed boost to melees because they are the ones that need it. Adc have range they don't need to out run you too.
Blood thrister: 75 ad, 20% life steal, passive that gives a shield for if your full health. Why does a clearly offensive item need a defensive passive attached? I feel this item should encourage you to go in deeper not stay out of the fray. Its a blood thrister so why not make the passive similar to warlords?
Sterak's Gage: Lets be real adcs only get it for the shield and this item still gives them damage and the shield is again passive. Either weaken the shield on range champs or make it scale with tank stats.
What I've noticed is that mericurial is being bought more often and sooner than before. In other season adcs usually bought 1 defensive item and it was usually their last item which offered little if any offensive ability. Now with mericurial, bt, maw, and sterak's they not only get defense from being bursted but get the offense to do more dps as well. I've also noticed that not many adcs build armor pen items quite simply because they don't need to. They put out enough damage and get enough pen on their items to counter any little a squishy may have built. Who cares how tanky a tank is when his damage dealers are dead.
I know people say mages double dip in offense and defense as well but the key difference is mages typically don't heal and they don't do dps not because they don't want to but because the itemization isn't there to support that style of play. Another important thing to not is a mages damage isn't guaranteed it may be hard to miss but there's always a chance unlike being right clicked on. In addition mages don't have 1:1 ratios on their moves so ap needs to come in higher values to do similar decent damage. And lastly mages don't get ap per level (except viktor at the cost of an item slot) or cdr per level stats they rely on whereas adcs get ad,and attack speed per level stats they value.
TLDR: Maybe we should take off some of the stats and adjust the prices accordingly for adc centric items and put in restrictions for range characters for items that both adcs and other classes share. Adcs have their place let the other classes have theirs.