Your skill sequence seems odd to me, the CD on Mace of Spades early on is too long for you to generate ironman effectively at all times. Grabbing more points in creeping death early on rewards you with a light hitting AoE that helps generate more Ironman and for longer periods of time due to the fact it lasts longer then the instant cast/hit of Mace of Spades AND increases your armor and MR while it's on. I'd say because most builds include a sunfire cape for Morde, if you're building a sunfire cape increasing your AoE potential means that youre always doing damage in a teamfight with the sunfire and Creeping Death applied. Your Masteries as well intrigue me. Morde already takes a lot less damamge due to ironman and self application of Creeping Death. Maximizing the potential damage you deal with your abilities means they generate more Ironman, more Ironman means less damage you recieve directly. He is a damage tank, I actually feel that his abilities lend him more towards being a DPS but most people build him as a tank, like myself actually. Morde's tanking abilitiy and effectiveness revolve around Ironman and to decrease your damage to provide survivability through the tanking tree means you're gimping his centerpiece, IRONMAN. Morde is literally a damage tank so you become a hard to kill DPS demon with the ability to disrupt enemies in a teamfight by causing a lot of damage so much so that you become focused by the enemy team which is exactly what you're supposed to do if you're a tank. Just my thoughts, you see Morde differently from me or so it seems to me. If your build works for you grats.
Rant over.