#DO CTRL-F FOR "IDEAS" TO SKIP TO MY SUGGESTED CHANGES AS TO HOW TO FIX THE WHOLE PROBLEM AND BALANCE ADCS WHILE KEEPING THEM RELEVANT AT THEIR INTENDED JOBS
(PS: I am talking about the ADCs that go crit and attack speed into actually increasing DPS, not caster ADCs that are closer to assassins or AD mages, like Lethality Varus or Jhin - whose attack speed can't increase like a standard ADC - and such)
It doesn't matter how fed the ADC is. It doesn't matter whether they're one item or six full damage items without boots and 100% crit and highest possible AD for an ADC with 100% crit.
#As long as the ADC is not massively ahead:
It doesn't matter what point in the game it is. Everyone else will be lategame by the time an ADC hits lategame level number of items. They still shouldn't be able to near instantly delete even the squishiest of targets. That's not their job at any point in the game. Ever.
Armor reduces damage but the bonus armor pen from a Last Whisper item or one of its upgrades allows DPS to affect tanks while not affecting squishies because it is only towards bonus armorpen. Well, ideally at least.
However, they should not be outperforming assassins and mages at their own job of near instantly deleting squishies. For comparison, let's assume a lategame Zed has 400-500 AD. With his armorpen he can do pretty high theoretical on a squishy without armor built. His Q has a 90% bonus AD ratio with a 210 base. Assuming 300-400 bonus AD, averaging at 350, he will do up to 525 damage with one Q. Ashe has 79 base and 9 armor from runes most likely. Zed will most likely have around 30-40 Lethality because Edge is still situational and fairly poor. That reduces his Q to around 372.
Zed's Q is the more or less equivalent of an autoattack. Shouldn't do much by itself and is part of a larger overall thing. But an ADC does 600-900 damage with one autoattack lategame pre armor, while spitting those out far faster. Yes, Zed can do is overall burst faster because he uses multiple abilities in succession in addition to shadow replication of the abilities.
However, an ADC can do Zed's equivalent of his entire burst combo in just several autos which will take just barely 1-1.5 seconds or so longer than Zed to accomplish. And unlike Zed, they're not limited to a long cooldown for their burst combo, they continuously spit out that damage per second endlessly.
Now this is purely from autoattacks, not even any abilities that just about every single typical non AD mage ish ADC has. With their abilities, they can reduce the number of autos it takes even lower.
Why play an assassin when ADCs do it better and at range safe and protected by Exhausts, barriers, shield, CC, and peel?
#IDEAS - MY SUGGESTED CHANGES FOR HOW TO KEEP ADCS RELEVANT AT THEIR INTENDED JOBS WHILE REMOVING THEIR UNNECESSARY POWER AT JOBS THEY ARE NOT SUPPOSED TO BE GOOD AT
1. Give squishy champions far more base armor and armor per level than they do now. Do not give that to tanks. Instead, boost the amount of armor tanks have on their ITEMS a massive amount.
2. Increase the Lethality to compensate for that (so for example, 40 Lethality instead of 18).
3. Give ADC champions some way of gaining scaling bonus armor pen (scaling on their own level), drastically reduce the current damage they have, but make the damage exponentially increase as they autoattack. PREFERABLY on items WITHOUT Lethality so that ADCs will be FORCED to buy those items (it can just be incorporated into standard ADC items like Zeal/IE/etc) if they want DPS over burst.
What this will do is:
1. Still let assassins do their job by having enough armorpen (because the higher Lethality to the higher base armor/armor per level will still do the same job as with lower Lethality and lower base armor/armor per level).
2. Kill off abuse cases of ranged champions using items they're not supposed to, to an abusive extent. They will still be able to use them, but in return, their DPS will be even lower so they still can't do hybrid BS. For instance, a Varus could go standard ADC build and reap the benefits of the exponential damage in lategame, but they will lose the damage against squishies for the first several autos. Or, they can go Lethality anyways and have large, assassin-like burst damage, but in return, their DPS will be absolutely gutted, because they will not have the DPS items and the bonus armorpen. So they will essentially just be an AD mage and thus lose all of their DPS, as they should. Or like with the first example, if they go standard ADC, they will have massively exponentially scaling DPS, but they will lose the burst against squishies. AS THEY SHOULD.
3. Still let ADCs do their two jobs (and what should be their only two jobs) perfectly well. The exponentially scaling damage means their first few autos will do far less impact on squishies, which is the point. However, said exponential scaling and their scaling bonus armorpen they will receive will make up for it against tanks, which is the people ADCs are supposed to focus anyways. And after they PROPERLY ramp up, if they focus squishies, they will still kill them quickly. But not before, which is the POINT.
4. Leading off the above point, their damage against turrets will still be just fine because they are supposed to ramp up damage anyways. The longer they auto, the more damage they will do, including against turrets, and potentially burst them even faster than before. However, they will not gain that immediately in the near burst-killing towers way they already have from the very first second. As they should.
5. Buff tower health, give them more armor, but treat said armor as bonus armor so that ADCs will properly work against them lategame, but reduce the massive snowball in early from everyone shredding them like toilet paper.