I main Teemo, and even he has more base movespeed than Mordekaiser.
http://leagueoflegends.wikia.com/wiki/Mordekaiser Mordekaiser- 325 base ms
http://leagueoflegends.wikia.com/wiki/Teemo Teemo-330 base ms
http://leagueoflegends.wikia.com/wiki/Mordekaiser Mordekaiser- 325 base ms
http://leagueoflegends.wikia.com/wiki/Teemo Teemo-330 base ms
Ur point being? Teemo also has a passive and active movespeed abilities
Why would Teemo be slow? I think 330 is too little to be honest. He's a scout. He's meant to be fast. Morde deals deadly damage close range, so he has to be slow. He also purposefully synergizes with Rylai's, so that is taken into consideration in his design.
You don't even play mordekaiser. I'm also sick of malicious metal constantly complaining about Morde despite maintaining a 55% wr.