Her CC is better. Her burst is arguably stronger in that it can come down over a much quicker window. Her ult is lower cooldown, and not to mention her ult being faster moving and thus better for snipes and objective steals.
Also, Ziggs isn't as good at protecting allies as Lux is. Her shield is kinda nuts if you can hit at least 2 people plus yourself.
Oh, and Lux is arguably better at poking in lane as she can poke past minion waves. Ziggs has to get much closer to lob his Q past minions. Lux E goes right past them though.
Not saying Ziggs isn't stronger, just saying she does stuff he doesn't do.
EDIT: That said, I agree with your proposed E buff. Interface and controllability should never have to factor in. Riot should impliment this QoL change. Also, I don't even think it would require nerfing her. When well played Lux is already this strong. It would just let more players access that strength.