Unresponsiveness of Lux's E and her mana costs

Hi there! I've recently started playing Lux and I find her incredibly fun to play. There's a few things I'd like to talk about though. (TL;DR at the bottom, as always)

The first thing that I find off-putting is the responsiveness of her E, or should I say the lack of it. When you try to throw out your E and immediately detonate it to harrass your enemy, the detonation cast feels unresponsive and has quite a noticable delay, often allowing your opponent to react and step back, leaving you with less mana and no profit. I don't know if it's intentional or not (probably not because it's quite responsive on rare occasions, especially if you throw out your E and let it sit for a second or so and then detonate it. In that case, the detonation is immediate). I used to think this only happened to me because I have a poor connection until I watched a streamer (I think it was Imaqtpie) play Lux and he also complained about the unresponsiveness of her E.

Second is her high mana costs, especially the costs on her E. (The E just can't get a break, can it?) Her E's mana cost starts at 70 mana, increasing by 15 each time she levels it up. That sums up to 130 mana per cast at rank 5. I personally find it way too expensive, especially since you usually level it first and 130 mana per E at level 9 is just too much for someone whose mana pool isn't that impressive in the first place, not to mention that it's a medium-speed skillshot, that (coupled with my previous point about unresponsiveness) often may not even hit the enemy, leaving you with no reward after sacrificing a whopping 130 mana. Even with Athene's Unholy Grail as my first item I find myself running out of mana all the time, and I'm not just throwing spells out like it's nobody's business. I'm actually being more careful with how I spend my mana than I am with most champions that use mana, such as Orianna. ** TL;DR** From what I experienced, Riot should tweak her E as the unresponsiveness is probably not intentional, and I also think that her mana costs are a bit too high for someone whose kit is exclusively made of skillshots, meaning it's not even guaranteed that you'll hit your spells, often leaving you with high (mana) sacrifices and low rewards.

Thank you for reading and I apologize for any grammatical mistakes, as English is not my first language. (: