It can be used pretty often and multiple times.
Scholar is more MP efficient even on something like chaining puddings. Kaeko did the tests and has posted most of what Tav has come up with and more back in March... here is the post
http://kanican.livejournal.com/26917.html#cutid2
Tav's numbers are great and his Nyzul uses further expand the job. However everyone wont be able to output the damage he does because he is another level of Blm and Sch than most.
I am a bit curious to see your resists parsed on Ix drk... not saying there were a ton but even I get some here and there so if your average ele skill on drk is less than mine I'd expect to see more which change your DoT. Perhaps insignificant but nobody ever posts their resists just their top dmg and I feel you can sometimes get a skewed perspective.
As for Scholar on something where u need alot of Ele skill... scholar is unlikely to keep up with Blm but they can turn Love black which looks really cool and is all that matters

I had a pic but its on the wrong computer
Scholar is getting close to the needed elemental skill for highly magic resistant mobs... a piece or two with + Ele skill in future updates and they will be there. Still the job is so versatile it's amazing.
Tav on floors where it says eliminate all enemies have you tried giving everyone AoE -en spells? It seems to work well in salvage so I figure on those floors only it will as well since the mobs have such low HP/Def/Eva etc.