Lux is only strong because of aftershock. Surprise surprise, broken keystone breaks another champion. So tired of people calling for nerfs but not knowing what to nerf. Lux is literally average when she doesnt go aftershock.
Similarly don't nerf karma, just nerf klepto. |(Although maybe push her out of top lane and make her a decent mid laner again kthx)
Hell i'd even say you dont even have to nerf irelia or any super strong duelist when it's essentially conqueror doing these things for them. I kinda miss runes and masteries because it was very rare when runes and masteries were broken (in fact ive been playing since about season 4, and i dont recall a single time runes were ever an issue, aside from that bullshit cost.
Masteries of course were tweaked and stuff but they also weren't super outrageous if memory is serving me correctly.
Tl;Dr Just nerf the runes, see how it goes and if it goes poorly then look at the champ. Let's not just gut champs because of a rune synergizing too well.