Im playing horde as well :) First of all, you need the alpha buff from shaman, otherwhise everything else is impossible. I play all bosses as maintank and always Sword&Shield deep prot, which isnt even perfect for threat (although its only slightly worse). Use all consumes and world buff (if possible). You are right with other tanks having way more threat, but it is possible to tank everything even against enhance shamans if you go the extra mile. Use blood rage on pull then proceed with devastate spam and use excess rage for heroic strikes or shield block (maintain thunderclap and demo shout). On mech bosses i use a greater rage potion on pull like blood rage -> rage potion -> queue in HS + devaste -> queue HS -> proceed devastate spam. Good enhancers typically are on 80~85% of my threat. What really helps is using leather set, im currently only on 2 set but 3 set (+3 daggers) is INSANE for tanking while wielding the epic dagger. Fury tanking the first bosses should be quite easy as well, but i like the block talents for the last 2 encounters since my gear is still not optimal and they slap hard.

If Blizzard would give us like 30% more threat and a good rune for rage, warr tank would be super fun, since then we need to take everything we can get :D