I just faced an MS-stacking Lux with Barrier. :/
If you haven't seen cancer, that's about more cancer to deal with than...something really cancerous. Lichbane, Ludens, Alacrity boots, Janna passive at times, 3rd dragon buff (with the 5th sometimes taking effect), and possible MS quints. You just can't catch her as melee without Alacrity+Deadmans+maybe a Zeal...or being Udyr. Other than that, she got somewhat fed off my downs midlane teammate who was Annie so even chasing her was dangerous when she had mana. And when you do avoid her skillshots to catch her, she has a shield and a snare coming up soon cause cdr lolz.
Why Riot thought it was a great idea to buff one of, if not, the safest AP midlaner is beyond me. The passive buff is all she needed..not the Q or E buffs. Those are just tacked on bonuses...Similar to Xin's crit. He is my fave jungler (pre-6.3) but he doesn't build IE or crits normally (or, well, I don't)...so it's not like it has great synergy. The AD ratio I would say is ok. Maybe.