Contrary to popular belief
the role of an ADC is to provide range and safety of dps to Towers and neutral monsters
It's not to get a penta 1v9 and solo carry the game
it's a strategic element to snowballing
AP champions lacked Turret damage with the exception of champions like ziggs that had in-built auto modifiers that proc on turrets
When riot wanted to break up the 100% ad marksmen requirement they decided to have champions transfer a portion of their AP to auto damage to turrets
it wasn't the base stat nerfs to adcs that broke that 100% requirement those were there to artificially force people to try out mages in the bot lane.
a placebo nerf if you will
Every role in the game has seen vast shifts in champion viability except for ADCs
The only shifts in power in the ADC role were between specific marksman champions and not actual types of champions
With the addition to convert ap to auto damage to turrets ADCs are no longer a must have and thus good for the game
now some champions are kinda insane with it but oh well
ziggs and veigar 1 shotting turrets it's just an unfortunate side effect