Well....if your LS is thinking BLMs > SMNs on Tiamat, I think that kinda speaks enough on the strategies and job choices of your linkshell.
I mean obviously a mob with a high magic defense and average physical resist, and horrible AoE TP moves, my job of choice would be the BLMs spamming spells and TP... [/sarcasm]
I believe I posted on here the example before that the only job that could even touch me on a early morning with me as the only SMN was 2 top geared DRKs. http://www.dakpluto.net/tiamat110107.html
One was a K.club DRK, other Merc. Kris. I came within 6000 total damage of the Merc. Kris DRK. BLMs did a whopping 3%-5% more than the tanks....
Only reason you should ever use BLMs on Tiamat is if you are doing the sleep on land -> nuke in air method, which you should only do that if really short on people or just really like taking twice as long to do a Tiamat.
Cerb...eh, Melee can do better, but are just stupid to have to heal through it, and TP gain on Cerb can get really bad at times. Still best to have SMNs doing the bulk of the damage and have melee as SAM or /SAM and rotate in for WS damage only.
Khim, see same as above with Cerb. Melee = stupid. They should only be coming in for WS only. Between Dreadstorm, Mist, Thunderstrike, etc you should never be building TP on him. Melee should only come in for WS only. And even then your melee of choice should be BLU. If a moron showed up DRK to our Khim I'd tell him to warp his ass back home and switch to a job that will actually be of use to us. So again, your best DoT....SMN. BLMs are stun only as Khim's magical defense is completely stupid, and even worse if you haven't broken the wings. Fortunally Fulmy isn't as stupid as Gates, so can normally get by with 2 Stunners.
Sandworm: yeah, wouldn't bring a SMN within 100 feet of it. It is a pretty crappy job for it. All the inside mobs are really best done with an old fashioned SC -> Massive MB method. (Well, kinda exception with Lambton, but can still be done if careful.) Obviously with Lamton, a bad timed P.claws can pretty much make you cry as you watch it heal the worm for 10-15%.
Ixion: yeah, plenty of TP mobs, weak in the rear...SMN is "ok" damage, but really best replaced with /THF DD.
Vrtra: well, right now the best strat is....well...ignore it (unless they finally un-ninja the stupid draw-in change) If they haven't fixed it, then really unkillable anyways as you can't kite or even straight tank the bitch anymore. Good job SE....
Fafhogg: I'll make the claim right now. You got RR with Magic Attack, capped Magic Attack merits, and capped Wind Blade or Thunderstorm, you are now the best DD there. Between a stupid low resist rate on Merit BPs on them, great damage, and MBing, we now own. BLMs have to back off because of hate...we don't. And no BLM is going to touch an average of 1400-1800/min damage with no stop. However...the only reason why I balk at bringing a ton of SMNs to DA now.....god we suck at claiming...seriously we need something better than Dia for claiming :\
I still find plenty of uses for SMN in Limbus (more Temenos than Appolyon though.)
Now, without a doubt there is places where SMN is worthless (but lots of jobs suffer that.) But if your LS is completely ignoring SMN now, they are making sh*t a lot harder than it needs to be.