[{quoted}](name=Dr Delusional,realm=NA,application-id=3ErqAdtq,discussion-id=KaFl0Tim,comment-id=00000000000000000000,timestamp=2017-09-09T08:01:30.066+0000)
I don't think you understand how little it does in comparison to the other supports. If the mastery is THAT useful, there is also nothing stopping the support champions from using it. All of their Q's can do the same thing as her E. You also can't reliably land Lux's shield on every teammate every time. EVEN IF YOU COULD, it isn't nearly as game changing as a thick juicy shield on your priority targets. Let us not even get started with Lux's lack of peel.
Lux doesn't have a defining identity in this mode that makes her a better choice over anything else.
Your team needs a support? Pick Janna or Soraka
Need an ADC? Pick Jinx or MF
Need a mage? Pick Syndra or Ahri
Need a tank? There is only one option... :D
Lux isn't better at anything. You can make her work in plenty of ways but you can make every champion work. Here, we are not talking about making champions work. We are talking about champions that can dominate their corresponding identities with the least amount of effort.
Lux is by far one of the best picks and a must have on any team that wants to clear onslaught. With a team of Miss Fortune and Jinx, she can consistently apply the ardent censer buff to each of them if they coordinate, while also having it on a 6 second cooldown with 40% cdr max rank.
Her shield is especially strong in any condition that requires you to stay inside a small area, you almost always get the double proc, and it applies to every member of your team. The only situation where a Janna/Lulu shield might be better is in the open wide maps where your team is split up to kill each enemy.
Stoneborn Pact applies to every champion that even walks through the E aoe, which makes it so you can place an E forever (keeping it there, and using it again) in a chokepoint within the stand your ground levels. In other types it isn't as strong but it still provides a large amount of AOE damage along with a slow.
I don't have much to say about her Q, but it can cancel Vel'koz's and Kog'maw's channels, and leave them vulnerable to your team.
All the while you're racking up athene's charges with your Q, E, and ult. Her ult is amazing, it has a very short cooldown on reset (which you get a lot of), while also nuking a large aoe. It's also useful for taking down far away Vel'koz that your team couldn't finish off.
The sheer amount of sustain and survivability she can provide to a team of two ADCarries like 
and 
that are building 
and 
while also taking fervor is honestly just insane.
The other champions provide a lot too, (besides Ahri, easily the worst pick in the gamemode) but don't make the mistake that Lux isn't a strong pick. However, playing with these masteries and builds in mind requires you to pay attention to everything going on, which is certainly a challenge. Also, sure the other supports can use it, but cannot apply it in the way Lux can.
Btw: writing this in a very tired state.
