I'm looking forward to Riot's explanation of why they're reverting this mechanic

Lux's ult got a partial reset (CD refund) starting in 7.7. Here's Riot's explanation for adding it:

Lux is great at picking off enemy champions, thanks in no small part to Final Spark. However, the high cooldowns on her kit mean that even when she's sniped a priority target, Lux is left without enough tools to reliably convert that pick-off into a greater advantage. This can lead to scenarios where Lux stalls out a game without the firepower to actually close it out. When Lux really nails her fights, she'll be rewarded with a faster recharge on her most threatening tool so she and her team can more immediately press the lead.

Basically, Lux was a bit of an ult bot who ulted and then couldn't do enough to follow up on the results to actually accomplish anything.

Here is a list of changes specific to Lux since that time (taken from the wiki), in chronological order, earlier changes first. Buffs have a + and nerfs have a -.

• + Magic resistance growth increased to 0.5 from 0.
• + Light Binding: Cooldown reduced to 13 / 12.5 / 12 / 11.5 / 11 seconds from 15 / 14 / 13 / 12 / 11.
• + Prismatic Barrier: NEW EFFECT: Hitting an ally with Prismatic Barrier as it's going out doubles the shield granted when it's coming back.
• + Base health increased to 490 from 477.72.
• + Health growth increased to 91 from 79.
• - Base attack damage reduced to 53.54 from 53.544.
• - Base health regeneration reduced to 5.4 from 5.424.
• + Base health regeneration increased to 5.5 from 5.4.
• + Final Spark: Cooldown refund increased to 30 / 40 / 50% from 10 / 30 / 50%.; NEW EFFECT: Cooldown refund now also applies on enemy champions who die within 1.75 seconds of being hit by Final Spark.
• - Health growth reduced to 85 from 91.
• + Base mana increased to 480 from 384.
• - Mana growth reduced to 23.5 from 47.
• + Base mana regeneration increased to 8 from 6.
• + NEW: Now has 7% bonus attack speed at level 1.
• - Attack speed growth reduced to 1% from 1.36%.
• + Light Binding: Base damage increased to 70 / 115 / 160 / 205 / 250 from 50 / 100 / 150 / 200 / 250.; Cooldown reduced to 10 seconds at all ranks from 13 / 12.5 / 12 / 11.5 / 11.; Mana cost reduced to 40 / 45 / 50 / 55 / 60 from 50 / 55 / 60 / 65 / 70.
• + Prismatic Barrier: Returning wand now always shields for twice as much, instead of needing to hit an ally first.; Now shields herself and fires the missile at the start of cast, instead of after the 0.25 second cast time. She is still rooted for the cast time.
• - Lucent Singularity: Missile speed reduced to 1200 from 1300.; Radius reduced to 310 from 350.;
• + Lucent Singularity: Mana cost reduced to 70 / 80 / 90 / 100 / 110 from 70 / 85 / 100 / 115 / 130.; Cooldown reduced to 10 / 9.5 / 9 / 8.5 / 8 seconds from 10 at all ranks.

Wow, what a great audience pile of buffs (mostly intended to see if a mid mage could be viable without one-shotting a wave, from what I hear)! The nerfs are mostly to her base stats, and then primarily to her capacity for autoattacks and defense. There's only one nerf to her actual abilities: E's missile speed and size were reduced... in the same patch that reduced its mana cost and CD. ¯\_(ツ)_/¯ The key thing to note in this list of changes is (in my opinion) the drastically lower CD of Q and E, from 15-11 and 10 to 10 and 10-8. That's the equivalent of starting with a CDR item for those abilities, and then being able to buy more CDR on top of it. The ult CD refund was, obviously, a similar change, reducing her ult's CD in many cases.

Do Lux's damaging base abilities still have high CDs as patch 7.7's context explains? Well, that's a subjective question, but the answer to whether they are now lower by around 20-30% is a factual "yes."

However... of late, Lux has started to see more popularity with Aftershock, which, even after the change to amplifying the user's resistances rather than providing a flat boost, is apparently still a problem on squishies. I'm wondering whether the ult CD refund is being removed due to Lux now having much shorter CDs or due to Aftershock. I'm additionally wondering about how Riot will explain the removal: will they blame Aftershock, shorter base CDs, or some other thing entirely? Will the ult CD refund be labeled as some kind of mistake that is being corrected via removal, or are we pretending that even directly opposed changes are just a series of improvements?