Morde isn't flawed, you just play him different than other champs.
At the beginning, hes kind of a "high risk - high gain" char. If you mess up your passive and catch every harass ability flying around - yeah, your screwed. If you push too hard to their tower in early game and their jungler (or whoever) decides to give you a spank, you better have your Ghost ready.
But hide your kids if someone makes the mistake to let Morde farm without harassing him in any way. And his ult? Consider the %-dmg of maximum Health it is doing, while healing for the same amount (use this on Vlad or Mundo..) Throw in some Armor and MR plus his shield and you have a walking blender-tank which is able to squeeze out some ridiculous damage.