He's a juggernaut, so he's supposed to be countered by kiting. Unfortunately, the other juggernauts have things like MS boosts and CC stronger than
to help them. Morde, in return for having a greater weakness to being kited with no CC, hardly any mobility, and a base movement speed that would make a mountain laugh, is supposed to make up for that with tons of damage.
Which he had... until 2015 Worlds rolled around, he was 100% pick/ban status in the bot lane, and Riot hit his kit numbers so hard it would make a mathematician wince. Morde was later compensated for the nerfs by being allowed back into a solo lane with a W that could be cast on minions. This was not enough to make up for what he lost, and Morde has been floundering ever since.
On one hand, having pre-nerf Morde charge the third Q strike, flash, and murder a marksman with (literally) one hit may have been too much. On the other hand, Morde has languished for over a year as punishment. His kit is in shambles. W still has the bonus XP passive that hardly ever sees use. When's the last time you saw a dragon ghost? Hell, when's the last time you saw a Morde? The guy has a 1.8% playrate; which is quite impressive... if you're Urgot or Galio.
Morde needs more than a minor look, he needs a second gameplay update. One that is not designed to make him into a duo laner.