It's not like Lux has tankiness, a dash, % damage and massive displacement. Apples and oranges. Take away her damage, and she's nothing. Take away her range/safety, and there goes the reason to pick her over Ziggs or Vel.
But maybe this change could maybe be applied to Lux's AoE instead? Make it start at 275 (used to be 300 before its latest buff) and go up to 375 over the duration if she really needs changes? She'd still hurt, but you'd have more space to dodge it. Although IMO she's not really that bad. Sure, her E poke is annoying - but if she misses her snare (which is slow enough to leave some space to outplay it) you can punish her severely for it.