A majority of AD carry mains don't seem too happy with the current state of their role in the game claiming that the new preseason changes nerfed the impact marksmen used to have.
The new item overhaul in the new League of Legends 2021 preseason has brought vast changes that turned the game's balance on its head. There were a couple of hotfixes but the problems are far from solved.
Besides the obvious bugs that naturally occur with changes of such a scale, the biggest problem the majority of the community seems to agree upon is the low impact AD carries have at the moment. One of the biggest problems seems to be the overall nerf to crit items stats - the items are less now less gold efficient as they provide weaker stats for more gold, at least compared to the old items.
To be fair, this isn't specific just to the AD carry role since all of the other classes seem to suffer from the same problem. Riot's goal was to compensate for these stat nerfs with the addition of new stronger passives. However, AD carries can't really use these new passives as efficiently as most of the other roles.
The somewhat iconic and common way of playing AD carries where play safe and scale for late-game doesn't seem to exist anymore. Now you don't get the same feeling of reward once you successfully "survive" the early game. The infamous bot lane mage meta could make a return considering that mages top the win rate charts for this position.
Riot's balance team will most likely have a hard time balancing this role between solo queue and professional League of Legends. The Marksmen role could suffer from the infamous "Azir syndrome" in which Riot has to balance this complex champion in a way that he's not overpowered in the hands of the very best players. This ultimately results in an atrocious solo queue performance since most of the casual players can't use Azir's full potential.
Having one "unplayable" champion surely won't break the game, but when the same issue gets extended to a whole class, that could become a significant problem.