My MAIN issue with Riot's mentality behind their initial Mordekaiser changes (nerfs).
But since DFG is gone, Mordekaiser has run into trouble in the late game because one of his essential play-patterns (blow someone up for a ghost) no longer functions well there.
I don't understand this. They think Mordekaiser is a Burst Mage. He's a Bruiser. He's an immobile, Magic Damage-dealing Shyvanna. The closest relatives to Mordekaiser in the '(Immobile) Burst Mage' family are Veigar and Syndra - but they have HARD CC, are ranged, and have more reliable damage. You can't call Mordekaiser a Burst Mage when half of his ultimate is a slow-ticking DoT ability.
Nowhere in my build (at least since Season 2 when I was still VERY new to LoL) have I ever built DFG. HE'S A BRUISER NOT A BURST MAGE.
Mordekaiser's only real weakness is his lack of Mobility and, if you really feel this is an issue, Hard CC. I beat the likes of Riven, Renekton and Rumble in the Top Lane as Mordekaiser consistently.
So much of this I simply overcome by picking him in specific team comps - usually when I have ally champions that can supplement my lack of mobility (Lulu, Thresh, Sivir, etc), and/or ally champions that can focus down a target that I ult to BOTH a) provide compound burst AND b) guarantee that I will get a ghost from my ultimate, at an optimal time (i.e. for as much of the duration of the teamfight as possible).
It's actually really awesome to ult a melee carry/ad assassin, W them, and walk them into the enemy backline with Rylai's + Liandry's ticking away.
EDIT 1: Also, here's a link to a thread I made in response to your initial plans for Mordekaiser (which you either never saw, or blatantly ignored because here we are). http://boards.na.leagueoflegends.com/en/c/gameplay-balance/FjEE1Vfy-riot-meddler-a-response-to-your-response-about-mordekaiser-post-dfg-removal
EDIT 2: F%cking AP Malphite was stronger than Mordekaiser with DFG.