I always find it humorous that ppl say you must be con/thm to solo things especially this. Almost every skill is cross class and almost every job's main weapon has decent magic acc/potency points. I'd rather be a LNC with 50thm/con subs then be a 50thm/con facing this NM and many others.
Personally I find this armor far superior in most group situations for lancer mainly due to the fact that stats are just so broken right now. We hit any visible cap on STR/DEX so quickly I prefer the att/acc. I sacrifice 50defense when equiping this over my vintage haub+2. But for the 5att/acc I think its the better choice as long as i'm not the main tank.
This body and the elmo helmet seem like a nice combo.
It's not really CON as much as THM, and the reasoning behind it is THM is kinda a broken class at this point in how over-powered it is. The thing is, the dots available to THM (Poison, Dia, Bio) don't scale the same way the mobs do. So, for example, you can do a regular hit on a marmot for say 500 damage, but on an NM you'll only do around 40ish. That does not apply to these dots, so if your Dia ticks for 100 damage each time on the marmot, it'll still tick for 100 damage on the NM. That, coupled with over-powered abilities like Emulate, Shadowsear & Firm Conviction and you've got yourself one powerful little mage.
As for all abilities being cross-class, well, yes and no. Some abilities do require the weapon (ie: Lancer's Speed Surge, Archer's Trifurcate) to be usable, but anything that -is- useable cross-class also takes a penalty. Usually the affect/attack power is not as strong, the cooldown is usually longer, and the buff timer usually shorter.