For those who don't, LoL always had the feature to have a black outline in the champions. This is usually used in games where the characters are really small on the screen (e.g: LoL, Super Smash Bros. 3DS) or cell-shaded games (e.g: most anime games like Naruto and Dragon Ball, Okami). Since the release of Kayn, Riot has been removing this with very few exceptions (e.g: Xayah and Rakan). This not only makes the characters harder to see (at least to me) it almost makes them blend with the background, making them more unnoticeable, which can end up in a death because we weren't able to notice the enemy in time. It also makes the game look worse. Cell-shade graphics makes games look good even after years (e.g: Okami) and, although graphics isn't what's important in LoL, it makes the game look worse.
I know sometimes it's necessary to remove it because you want to do those "flowing-transparent hairs/capes" like Shadow Assassin Kayn and Katarina's last Harrowing skin but Irelia really didn't need to have the inking removed. You should take a Yorick as an example: he still has the inking and still has his transparent cape flowing.
TL;DR: Riot has been removing the character inking from champions, which makes them harder to see.