I'm not high elo player, and not meta-abuser, not LCS-follower. Just an average player, who played a lot with Lux (not even maining her).
As far as i am concerned i play her only mid. Her shield nerf is accurate, playing her as support and spamming spells with success is not a playstyle anyone should have, her range gave her no risk but give her high rewards as support. But only as support. In mid lane she was quite vulnerable in a lot of matchups, mostly because of her inmobility, and the selfshielding has a delayed effect (shielding an adc from max range was broken, but lux always had only a little amount of shield, then 2 sec later another little amoun, cuz she got the earlier one disappeared. W/e, shield nerf is absolutely rational.
BUT WHY ULT RESET? T_T
Her mid-lane is kinda shity, if you face AP champ, it will buy zhonya and press it when you unleash the fullcombo. Assasins will dodge it, AD-s will qss your Q. There are options to counter her, and this is balanced. But back then they gave the ult reset, because lux is useless when ult is not available, her basic spells has decent CD so you don't have a lot of kits, you can run aways until they are back up. But when you hit a successful combo, and you delete the adc, with the ult reset, you can use again, in the same teamfight to dmg the megatank that will stay there and devour your team.
So i think nerf the shield, nerf the support, maybe give her Q more CD early, but her ult, for the mid-lane carry should stay the same. Because back then, when you could use ur ult in every 30 sec meant that, you can have an adc dead if you are lucky, otherwise go base because you are useless. With this aggressive mode, you can turn around teamfights with your ult. And having 80% ap ratio instead of 70% is not compensative.