Got back to back Lamentations after not getting any Legendaries for a while. Had to laugh.
I did craft a decent pair of gloves finally; I lost about 4k damage on them (shit Dex roll), but the gloves I was using had NO Vit or AR on them, and this pair had good rolls on both so I gained about 62k eHP which is completely ridiculous and worth the tradeoff.
I only did that act 4 run in PTR for curiosity since I refuse on principle to usually do PTR stuff (since I know I will get the drop to end all drops in it and it will kill me), but the same thought about no breathing room occurred to me as well. I can't remember, are the mob density increases only when you have MP active? If you're running vanilla Inferno it's probably a non-issue, and if you're running MP constant trash mobs are probably a non-issue, and if anything are helping you keep buffs/abilities up depending on your class.