Except the problem really is with ADCs as a class, even if some members are particular outliers. The fear that marksmen would somehow "fall off the map" if nerfed, stands out in stark contrast to the fact that marksmen have been mandatory to every team for over six years. There has literally been no time in League's history where marksmen have even come close to having their popularity endangered. This in many ways echoes the "ADC in 2k17" meme earlier this year, where the only very occasional instance of Ziggs replacing a marksman was enough for some to cry the death of class, and for Riot to send out yet another wave of blanket itemization buffs. This madness has to end.
When the issue of marksman balance gets brought up, usually statistics get mentioned as well, but the main issue with this in relation to marksmen is that most marksmen are only measured against other marksmen. Fighters, tanks, mages and assassins are all held up against each other in some way or another, and so are therefore in the same balancing environment, but marksmen in bot lane (and supports too, to some extent) only compete with other marksmen, because any other class that tries to take their place simply cannot compete in any way. When one marksman wins, another marksman loses, and I think it's this blindness to the meaning behind these statistics that has allowed marksman balance to be considered acceptable, even when it really isn't where it should be.
At the end, what people are asking for marksmen isn't really all that unreasonable either. Asking for less burst on a DPS class, less drain-tanking on a class that is meant to be squishy, and more outplay potential on a class defined by persistent unavoidable damage, is something that can and should be applied to anyone, and that has been applied to other classes in the past, such as fighters, mages and even assassins. Many of these suggestions benefit marksmen too: many players would likely be absolutely fine with having good marksman presence outside of bot lane (this was largely seen as a positive change when it happened after Preseason 6), it's just that these same players would also like more classes than just the marksman in bot lane, or as their team's carry. Many players would also like to take some stress off of playing marksmen, because all too often nowadays it's bot lane that gets both the full credit and blame for their team's victory, starting at the laning phase. Really, it's not so much about nerfing marksmen to the ground, or eliminating from the game, or any similar kind of rubbish, it's just a matter of making the game's balance and diversity far less rigid. Because of this, the fact that this is perceived an attack upon marksmankind by some comes across to me as very short-sighted, and not in any way fair.