Differentiating ADCs from each other
I've been really wanting to get good at ADC, so I've been spamming ADCs in normals (as well as Volibear whenever I want to get fed brainlessly). I noticed that most ADCs are similar except for Draven/Kalista/Varus. The biggest distinguishing factor between ADCs is their mobility, their range, and their damage. Their tankiness, CC, utility, etc. are very similar. Well that's just 3 distinguishing factors for 20 ADCs.
IMO, we should make ADCs as distinguished from one another as bruisers or mages are from one another. There's a HUGE difference in mobility, damage, CC, tankiness, utility and range between J4, Udyr and Nautilus. Same as the difference between Ziggs, Malzahar and LeBlanc. However, the difference between Lucian, Caitlyn and Graves is much smaller.
I would suggest more interesting ADCs like Kalista. Despite being extremely annoying, she is undeniably a very interesting champion.
Her 90% autoattack scaling with AD to make her rend-centric and to focus her on kiting and sustained damage, rather than lucky crits, is a design that is unique to all ADCS.
Why not have more ADCs with a similar mechanic that rewards them for maxing out on certain aspects of their kit? For example, for Lucian, give the Culling additional scaling with AS. Give it +5/10/15 bonus magic damage (+1 per 10% bonus AS) for each successive bullet hit, and make it a homing, point and click spell that ignores minions (but still blockable by enemy champions and still channeling) if Lucian reaches above 2.0 attack speed. This would mean that Lucian could either itemize as a regular DPS ADC and use his ult more or less as it is right now, or itemize as a bursty assassin with max attack speed but very low AD and weak crits compared to traditional marksmen.

This way, he can choose. Either take a traditional sieging/tank shredding ADC role, or take an assassin role that can (late game only) nuke a single squishy at long range if they are not protected, but sacrifices alot of tank shredding ability to do so.