The whole meta is in a weird place right now.
While lethality changes are a contributing factor, they aren't a decisive one.
CoC and low tank item costs ( compared to crit build ) is what brought the lethality upon us.
3 tank items+boots= ~9500
3 crit items+boots= ~11000
If you wana keep up to that tank you've got to peak earlier.
Lethality gives you that.
If they didn't buff it ADCs would be in a worse spot than they are currently.
As I said weird meta...
Probably will change even before the mid-season tank update ( I hope).