HM armour vs. Fire was always high. Also, I think that just proves that everything works in PvE, including using Searing Flames Eles vs. Destroyers ... it's just a matter of how fast / how stable the build is.
Nothing to do with Searing Flames / Invoke Lightning, but answer to that question is "no". As with all wards, you are better off splitting up than clumping together in a ward: it is less dangerous to have Savannah Heat hit 2 unprotected heroes than it hit all 7 heroes in a ward. Also Elementalists have decent energy management already, so Glowstone's synergy with Enfeebling Blood is minimal. Have Enfeebling Blood in your teambuild if you want, but unless for specific purposes (you are playing a melee character and are confident in your ability to ball stuff up, for example) don't bring the Earth Ele.
Thank you for your response. I was going to bring it for a Snake Dance vanquish anyway and that's all I could think too use it for. I personally prefer a prot. ele in any HM content, rarely bring invoke. But definitely invoke>SF.