Make Classes Multifaceted

[Ultimatecalibur]

Except the Gladiator uses reductive defense rather than recovery. The moment they are no longer getting hit or intending to get hit 12 of their 17 abilities are rendered useless. (However, the idea of a Dark Knight does work for the HP driven Marauder in a much more acceptable fashion, so you're not far off)

Only 9 (or 7 depending on your perspective on Convalescence and Tempered Will), not 12, would be "useless" (some of the others would be underpowered but not useless) as they currently are. In comparison a Lancer, a class with a surprising number of abilities that parallel marauder and gladiator, has 6 abilities (all of them attacks) that would be useless as they stand if it switched to tank and Doom Spike is gained far to late as a potential aoe threat generator for low level tanking purposes. It would take potentially the same amount of work to change the Gladiator into a dps as it would to Change a Lancer into a tank.

[Nahara]

It would take potentially the same amount of work to change the Gladiator into a dps as it would to Change a Lancer into a tank.

That's kinda the problem with the current classes, aside from Arcanist. They're all very single-minded in how they were built and it would take a LOT of tweaking in order to give them a second role. Unless SE decides to heavily revamp the classes later on in order to make them more flexible (or SE if VERY liberal with the changes that can happen to a class when a soulstone is equipped), we may not see any new roles added to the current classes.

[Tzain]

Only 9 (or 7 depending on your perspective on Convalescence and Tempered Will), not 12, would be "useless" (some of the others would be underpowered but not useless) as they currently are. In comparison a Lancer, a class with a surprising number of abilities that parallel marauder and gladiator, has 6 abilities (all of them attacks) that would be useless as they stand if it switched to tank and Doom Spike is gained far to late as a potential aoe threat generator for low level tanking purposes. It would take potentially the same amount of work to change the Gladiator into a dps as it would to Change a Lancer into a tank.

I assume you're talking about the 2 positional attacks.

Heavy Strike: It's a pure DPS increase. Thus, low priority to tanking. The follow up is level 46, which means 4/5 job skills are available.
Impulse Drive: Utterly useless until level 38. The combo attack it leads to doesn't require positioning. So it's currently feasible to do a Leg Sweep > Impulse Drive > Disembowel > Chaos Thrust without any modifications/additions.

I've had to Lancer Tank pretty much every dungeon up to and including haukke manor due to vanishing tanks. Which means we end up with only a 3 player team. I cross classed Flash, Skull Sunder, Bloodbath, provoke, and every Defensive Cooldown I could fit and cycled through them much the way I would on a paladin/GLA. Worked fine, although I admit I ran into some longevity problems on longer fights. One of the first things I noticed was the Doctore Gear from Halitali, All my tanks wore that armor due to it having the best stats at that level range, when my Lancer wore it he was nearly as tanky. As I replaced it with higher level DoW gear I was comparatively less comfortable. So opening a lancer job to the heavy armor use-list would go a long way with keeping things under control. If I had actual job skills to go with the cross class ones I brought in I'm positive it would work.