Dragoon vs Lancer, is there a secret benefit?

[Gamemako]

My question is, how effective would it be to be just a lancer at lvl 50 will full allagan. Another possibility could be a mix of allagan, phil stone armor, and myth stone accesories, cause the rings and stuff like that work for all classes.

The big sticking point is the weapon level. Unless you somehow get your hands on a Twintania drop, you're invariably hurting yourself. That said, DRG will outdamage LNC even after all cross-class abilities are accounted (only Raging Strikes is actually worth counting). You're going to have considerably lower DPS with LNC after you account for the lower weapon level. You have a bunch of traited notes in your work here as well. Traits do not carry over -- Raging Strikes has a 180s cooldown, Virus only affects STR and DEX, Mantra is 5% instead of 20% boost (lol), et cetera.

The only advantage you'd have on LNC, really, are cross-class debuff abilities like Virus, and I just don't think those are really good enough to justify the loss. LNC isn't much of a tank, and even ilvl90 Allagan gear has lower defensive stats than ilvl46 Tortoiseshell. No, really, that set is the very highest DEF/MDEF a DRG can ever get -- 126/126 for HQ Tortoiseshell chest versus 110/62 for ilvl90 stuff.

MRD is a bit of a special case in that it can stack out a bunch of multiplicative bonuses to deal massive burst damage. It has one of the few pure damage buffs that is not cross-class, and unlike GLA, MRD has the native abilities to do decent DPS. It's not a the greatest DPS in total, but it's actually pretty solid all told. You might actively see a bunch of MRD running around at endgame if it weren't for the effective restriction to ilvl70 weaponry. Hell, with 2.1, you may see it happen anyway.

//EDIT:

About the MRD though, don't they really need to become WARs for the tanking ability? If they just stay MRD then they lose out on wrath and the benefits from those skills. If a MRD did this, they would still have to join dungeons as a tank, but it would seem they would have major issues holding aggro, unless they were geared to the teeth, like full Allagan or Allagan with Hero accessories. That's just my thought, I am currently only a 20 MRD looking to become a WAR. T.T

Everything WAR does is related to Defiance. Defiance reduces damage by 25%, meaning you won't be using it when you want to deal damage. The point of using MRD is to have a super-durable DPS -- you aren't really tanking with it.