Unfortunately Katarina got updated as part of a Class Update.
Meaning like A LOT of other champions she suffered in regards to her skins not getting the attention they deserved.
Unfortunately Class Updates always seem to follow the trend anyways.
Which really sucks. Riot really undervalues how amazing skins are. At times I play champions because I love the skins they have, not just for the champion themselves. UNfortunately everytime Riot gets an opportunity to upgrade, they either don't or do the opposite.
Katarina saw her;
Sandstorm skin lose it's particles.
Slay Belle lose it's Shunpo Particles and other effects.
Project saw a general decrease in quality. (Colors were toned down significantly)
Warring Kingdoms saw it's effects toned down.
On a side note she did see model changes for her Q. Where each skin with a different blade now throws that particular blade instead of her classic. Nice change but not worth losing Particle effects over.
Sejuani saw basically the exact same treatment when she got her sloppy VFX's updated.
Hilariously enough Maokai saw ALL BRAND NEW VFX for every skin.
Whereas Sejuani lost VFX. Was really a true example of Riots lazy and bias as fuck side.
Poro Rider lost it's Subtle Particle changes.
Bear Cavalry losts SFX and her VFX became a recolor.
A lot of her skins models saw a downgrade in quality due to Frost Armor obstructing the models.
Unfortunately the skins team remained silent on the whole thing like usual.