Thats the thing with Darius. Once you get cced, you will get melted no matter what. The only way you can survive is to manage to Q three people and have
but keep in mind that you will be beefy later on. Darius needs to have a lot of tanky stats but he isnt really a tank compared to Garen for example. He has % damage reduction along with free 30 armor and mr with the cost of dealing peanut damage.
With Ekko, he has literally tank items.
/ 
With Darius, you are forced to get
for damage and
to not get bursted but that keeps you from having two actual tank items like
and 
Thats why you will see Darius build like this
/ 
If Darius never had to build
, he would be even harder like
, it provides you with 20% cdr and it will ensure that you never run oom and once youi caught up to someone, it will be tough for that person to run away from you BUT this will make darius even slower than before because you don't have your % movement speed like before, and in order for Riot to compensate that loss, they made his passive physical damage and make it extremely beneficial with
cuz one stack = 20 ms per second. BUT it will be harder to kill him if you had another item besides BC because BC does not provide you with any defense, but technically, it does provide you with some "def" by giving CDR in order for you to Q more often.
It's just this Season thats crap. Ekko is one of the reason why I'm waiting for Riot to fix up their game. Ekko has everything a tank/assassin would ever want. Shields, permanent slow on passive, dashes, stun, % health damage. If you see any tank top, you will see that they have some form of % damage along with CC or you will see a champion just named CC e.g.
. That is why the % health along with the metagolem items and Grasp of OP makes them nearly unstoppable.