Well, your big problem is that you're playing regular games. Nobody actually learns things from regular games.
People did the EXACT same thing when Darius came out and it took months for people to figure out "maybe I should play around his pull or I'm gonna get smacked."
Funnily enough I'd argue out of the new/buffed/reworked champs Morde now is actually one of the more balanced ones - he doesn't have bullshit mobility and he actually has to land rather slow/telegraphed linear skillshots. Sure, he can become an unkillable raid boss, but that's a number of different top lane champions. He's just being overplayed right now because he's the flavor of the month and he's the badass iron juggernaut.
Chances are pretty good he'll drop off once people learn how to play around him / move on to the next release.