i have 3 brutes, 2 scrappers, a blaster, a dominator, a corrupter, peacebringer, and a MM all capable of farming 4x8 fairly easily. I could probably create a defender to do the same. Its all about the build bro. im not saying defenders could'nt use some love (god could they) but with a little creativity and a crapton of inf a dps defender can probably farm.
As far as mag protection goes we have acrobatics and thats a mag 2 i do think it should be a mag 3, or at least can accept enhancements that improves its efficacy.