Damage reduction was removed because he is an assassin not a tank
is an assassin but has 15% damage reduction on a 6 seconds cool down but potentially no cool down at all when in a team fight due to passive.
The only champ that is allowed to be an assassin and tank is 
, riot pls nerf cat arena
Maybe it could be her compensation for DFG
JustMyBassCannon2 votesShort answer; she's always had the mechanic, and it's not really something that makes her ridiculous.
15% Damage Reduction, while it can't be reduced by penetration effects, is a really small amount of defense. Because it's multiplicative with Armor/MR, it's a very small steroid. If we were to assume Katarina didn't build more than 100 Armor/MR, Shunpo's %DR isn't even worth 35 Armor/MR. Compare it to every other defensive steroid; the only ones I can name off the top of my head that give less effective Armor/MR are Fizz's passive, Braum's W if he has less than 60 bonus Armor/MR, Taric's W before he has 300 Armor, and Shyvana's passive. There might be a couple others.
N3mO061 votesbecause she is must be tank to do a penta
Tsugaga1 votesKat is a mage though, so when her abilities are on CD she's nearly useless, it's not the same as a Kha who's auto attacking and sustaining with W and lifesteal.
Budupops1 votesher abilities and ult are all on low cooldowns
Tsugaga1 votesher abilities and ult are all on low cooldowns
If she doesn't get kills/assists then her cooldowns aren't that short, especially early-mid game, she's basically the same as any mage unless she gets kills/assists.
Budupops1 votes90s cd on ultimate is very low compared to other mages. Basically once she hits 6 and is against an opponent with no hard cc they have to stay under tower the rest of the laning phase, cry to jg, or die.
Marinaras Trench1 votesKatarina is in a fine spot right now, I personally don't think changes are needed, especially with dfg removal
Budupops1 voteswell she has a very high win rate in all divisions
The Troll King1 votesThe reason why she has high win rates is because players just in at the last second when the enemy team has used up all of their abilities. If she can get on the AP, Squishy Support (if the supp is even squishy), or the ADC, it's pretty much GG.
Jefftiffy1 votes
The only champ that is allowed to be an assassin and tank is
was a spammable 50% reduction a little bit different story there.
I still don't quite know why she gets it using it on an enemy team. Should only get it when used for defense. Plus 15% is that much against a real damage dealer.
8bj2yMEanN1 votesYea seems to me like they were just like "let's add on another mechanic cuz yolo" and then they added the 15% damage reduction.
No Plans Made1 votesIt doesn't stack if you spam it, + she has to dive deep in to teamfights. :/
Abyssphere1 votesKatarina's damage reduction is not making her a tank, it's a tiny amount on a squishy champion. It is just there to make sure the champion who needs to soak damage for 2.5 seconds to get off her full combo does not get blown up instantly. The reason other assassins don't have it is because most of them pick off a target, dash in and dash out. No other assassin's combo involves getting in the middle of as many people as possible.