Shadow Priests

Why are priests, the dps kind, so low on the dps charts as I level through content?  currently, I am at my mid 40s with my shaman and I've not seen a shadow priest beat my totem in dps. 

This actually kinda start when I started SM:GY and for 15 levels, I've been noticing the same thing.  my magma totem gets dropped, it pulses. and, if I have enough mana and don’t need to heal much, will blow it up. once, I was top dps. but that was just once.  other times, I've usually been very conservative in using my nova. I would place my magma totem down and let it pulse.  at the end when everyone's about to die I would hit nova just to finish everyone off before they start running too far.  this happens a lot in SM.  everyone runs away in fear.  its so annoying.  but this helps. 

What I don’t understand is why the shadow priests (and its every single shadow priest I tell you) do so much less damage than everyone elses (not just me, although I do enjoy being second to last, I don’t mind being last on the charts)?  in fact, once I posted the meters and asked everyone to please do more dps than the healer, and the s.priest decides to tell me to stop dps-ing.  in which I replied, I wasn’t, it was my totem.  yes, the only dps totem I have. one totem… can beat your sorry ass in dps.  and when the instance was all over, everyone beat me on dps and total damage.  except for the s.priest. 

Now I want to know a few things about these shadow priests that maybe I never considered.  I played one a long time ago and got bored of it quickly.  although there are "dots" to apply and some dark beam with a ripple effect thingey you guys do, I figured that's really all that's needed for dps in level 40 content anyway, correct?  I don’t even see mindflay (which was their signature move years ago) but now I see Deviouring Plague, SW:P, then Mind Sear.  Shouldn’t that rock the dps charts?  perhaps these guys arent into the whole AoE frenzy.  but that's not the point.  the point is to do the most damage given the situation, correct?  so if you see four mobs together, you bust out your Mind Sear.  If you see one, you'd be stupid to pull out mind sear.  correct?

Just like me on my paladin, one boss, Seal of Corruption.  four adds? Seal of Command.  easy to understand. one mob or boss, cast lightning bolt.  four mobs, cast chain lightning, drop magma totem and nova. chain lightning on cd.  for mages, one boss/mob, cast fire/frost bolt or arcane missles.  more than two, arcane assplode, blizzard, fire ground thingey.

see?  its very easy to differentiate between single target, and multiple targets.  you just have to… erm…. COUNT.  and then adjust your rotations accordingly. 

Am I totally missing something?  is it because the s priest was going to use up all his time alternating SW:P that by the time he was ready to mindsear, everyone's dead?  maybe.  mobs do die pretty fast. but so adjust!  I do this often with my warlock.  there are many times I know that my dots will not last its full duration.  and what do I end up doing? I improvise.  I only use one dot, then switch to some AoE if I can (seed of corruption/rain of fire) and woot! dere it is.   

So I do not know.  someone please enlighten me to shadow priest dps.  is there no other AoE alternative than to use DP, then SWP on everything, then Mind Sear?  I know this does take a while to actually accomplish, but am I correct to say that Mind Sear would still do a decent amount of damage even if everyone isnt "swp'ed" up? Am I treating shadow priests unfairly?

screenshots or it didnt happen?