Note, I'll be discussing the following changes:
Death Lotus [ R ]
* Cooldown increased from 60/52.5/45 seconds to 90/60/45
* Base damage decreased from 400/575/750 to 350/550/750
As I understand it, the goal with this change is to decrease Katarina's bullying potential in lane post-6 and her roaming. If you do that, you'll be deleting an already niche Champion from any sort of competitive play.
Let me iterate. Katarina has **zero presence** in lane before level 6. A player picks her for her roaming strengths. In rare cases, she can bully the other mid laner with the short cooldown on Death Lotus, but that's highly situational and most mids can cancel it and kill her afterwards (given Shunpo's long CD at early levels).
When Katarina's W was reworked, her power was better-spread across her spells. What I mean is, her Q-W-E would deal meaningful damage and her R wouldn't be completely overwhelming. Over-time, Bruiser Kata was nerfed and she went back to being a one-trick pony.
A 50% increase to the CD of her most important spell is a death sentence. You cannot expect Katarina to compete when the only possible way she can influence the game at any stage is with Death Lotus. This cuts down her ganking presence in the early game **by half**. That's completely ridiculous; it's the same as if you nerfed Ahri's ult by that much, it cripples the Champion.
The base damage nerf is acceptable, I suppose. The CD change, however, will kill Katarina. Consider how easy it is to counter Katarina. If you go with this change, you basically encourage players who never learned a Champion's **only strength** that they don't have to consider counterplay, that they can just expect these nerfs to be handed out without any consideration.
Katarina's had a close to 50% win-rate across Leagues; she was played ONCE on a competitive stage and it was PawN who played her, arguably the best mid in the world. There's zero reason to nerf Katarina now, especially this severely. Please, consider what you'd be doing to the Champion.
**[ SUGGESTION ]** If this change does need to go through, then buff Voracity to 20-25 seconds. This lessens the impact on Katarina's roaming and just prevents her from spamming Death Lotus in lane.