User blog comment:Obyvvvatel/Magic resistance isn't effective./@comment-9369480-20130516220932

Back when FoN was around, MR was incredibly effective. Spirit Visage is still a very viable item for fighting mages. When using an AD Bruiser/jungler, some lifesteal, SV, and a Wit's End make you unbeatable against mages.

MR is effective, just not viable. The lack of good builds (outside of SV, which builds out of Kindlegem which is great) prevents the valuable use of building MR items. Bulwark gets you 55 MR and some health, but it's really only viable on tanks and takes up a lot of item slots when building. Most MR items at full build take up several slots, which reduces effectiveness of building them since you sacrifice item slots for other, more valuable items.