User blog comment:Obyvvvatel/Magic resistance isn't effective./@comment-7557572-20130516214928

16 Champs have a way to reduce armor (most of which are by percentages), 12 champs can reduce magic resist (most of which are flat values). Black Cleaver also reduecs armor by a percentage whereas Malady (the mr equivalent to black cleaver?) reduces it by a flat value.

Also burst champs would be hurt with these changes.