Why is Irelia and Jax allowed to have...
the same tankiness as a juggernaut champion while also having tons of mobility and more damage?
There is a reason why juggernaut champions are tanky because they lack proper mobility and it is kind of hard to reach the back line.
So why can Irelia and Jax build the same usual items of Trinity Force + Sterak's Gage and get the same health pool as Darius or Garen, but also have more CC and damage reduction than Darius and Garen while also having tons of mobility and having more damage?
Why should I pick a juggernaut champion when I can play Irelia or Jax and do the same kind of tankiness, and also have more CC and also have more mobility and damage than a traditional juggernaut?
Why should I pick a full tank that has just tankiness and will die without outputting proper damage than pick Irelia or Jax that does the same job as a full tank but way better?
needs to be removed so they more squish
but can help you deal with armor heavy adversaries.
+
(to form a ad mana regen 5%cdr item) and 
and remove the lethality because there will be enough lethality items
give it 60 AD
~300 hp
and 5%cdr and 50% mana regen
also builds from the 
trifecta. It totals to about 1150 bonus HP. Then Sterak's pops in when they start dipping low giving them a 'second chance' with 75% of that 1150 for another 863 temporary HP to cut though.