Actually, a little off, Current Patch Stats, according to Champion.gg are as follows:
: 21.08% Playrate, with a 51.17% Winrate out of those games.
: 13.15% Playrate with a 53.05% Winrate
: 7.56% Playrate, with a 51.50% winrate
What these show is that people who actually PLAY lower playrate champions, have a greater success than with others.
Karthus Mid, where he's MOST OFTEN PLAYED is played by...1.23% of players with a 50.12% Winrate, meaning those few who still play him...have played him enough to do so WELL.
Kog'Maw? 1.26 in an ADC capacity, with 51~% winrates
Morde has, by far, the most dedicated out of the four you've put forth, at .14%, .16% and .75% playrate, in Jungle, Mid and Top respectively, and Sub-fifty Winrates, which honestly do show how bad of a state he's in right now, considering that the highest hovers around 47%.
The only reason that Morde, Kog and Karthus, Galio and a handful of other champions who aren't listed here have winrates AT ALL, is because of the 4-5 dedicated people like MaximumMorde and his ilk who STILL PLAY THEM.
For Jhin to have a +50% winrate while still being in the 20% range out of ALL the games played says quite a lot.
Also, oddly enough, Sion Support has the highest winrate in Plat+ games, sitting at 55.11%
http://champion.gg/statistics/#