The main problem here is not Darius killing squashy in 2 hits, any bruiser can do that. The problem is, as a melee, you get into a fight with him will mean that you have about 700hp less then you would expect.
Assuming you both have similar equipment (darius can build fairly tanky too and still has a high ulti damage), the armor and MR you built does not matter against him.
But if you only stack hp, you can beat him, but loose to the 4 other teamates he has
And mind you, Dominion does not have warmogs as some quick high hp item