I'm not saying that you'd need to have some sort of sub-set (or advanced job) of the Paladin job that takes a turn for the offensive, only that the fundamental components of the job should be such that it can play multiple roles given intelligent (not necessarily even "correct" per say) gearing.
Let's take this little example: a reflect ability and a cover ability (intercept an attack/spell). A presumably defensive ability now works potentially offensively, or at least outside a "tanking" role while also providing a supporting (defensive) element. If the CD for the reflect is shorter than the CD for the cover, then of course a true tank (or even a off-tank or snap-tank) would make better use of the ability, but unless it is heavily limited by one's defensive stats it can still work plenty well in both a non-tank party niche and non-tank gearing.
Additionally, I think the reason the class system of 1.0 left players feeling un-unique was the way the ability selection was handled. Had the difference in abilities been slightly improved upon, and ability swapping a bit less quick, it made us potentially unique machines of war, allowing us to focus on linear-cannon abilities, self-centered AoEs, fire abilities through both physical and magical sources, etc. But that does nothing to give substance to a class. In a way, that's from a very simple issue. Abilities then were not class-tied. They were class-gained, and from then on were mere floating selection choices. This would have been more apparent had the classes themselves had something unique, rather than being a level progression with a set of abilities to buy with experience. That said, post-reform changed relatively little in that point. Classes were cornered off from each other due more to the lack of physical level and some just having genuinely slower killing speeds than others than any real unique class mechanics until you were at least level 30 or so. Having an actual different feeling entirely within each different class would fix this issue, but that requires that a class be more than a bank of abilities, or at least that these abilities are highly adaptable.
In all honesty, I don't consider a class role as a unique identifying factor of a class. I don't expect a Dragoon to tank any more than I would expect a Paladin to main-heal, but I would think that it would at least have enough burst dps (for threat-stealing in this case) and mobility to make it a good kiter, and to me those features are what makes a Dragoon a Dragoon. As for Lancer, less specialized (but also lacking those unique features) than a Dragoon, I don't see why it couldn't potentially tank, if its range can be taken advantage of. Hold threat on the conical blasting boss and back off just before tp moves so the cone starts near your position, skipping over the closer melee, or just keep things behind the length of your spear, unable to attack you given the you and your party's stuns. Does this advantage make Lancer a tank? No. It makes it a melee with a long reach, and a primarily charging or tactile mindset (each half enjoyably diverse from the other).
If all that's possible in this class-job system, then I consider it good groundwork. Personally though, I still think that jobs ought to be more than solely the tip you put on the shaft of a class after having leveled it to make it finally effective. Jobs should be specialized variants that stem from one or more classes, and not just as an arbitrary 30/15 requirement check at that. If Dragoon should stem from a Pugilist, there really should be some feel that Pugilist captures about the "thrill of the fight" or "do or die" offensive evasion or the like that truly applies to what it is to be a Dragoon. A Paladin would certainly stem from Conjurer, but it's a bit painful when that stem only goes so far as "I have Cure" or "I have Sacred Prism". "Now, why does Conjurer have Cure?"
All that said, in most future class sets, I don't see jobs as being attainable from only one class either. Let's take Beastmaster for instance. Is there any reason why you can't fight alongside your pet with a sword or an axe or a bow rather than a whip? If you were doing absolutely none of the damage and you're pet all of it, then a whip might be reasonable, but then what's the class for it? And in the first place, why is the class actually needed except to fit a mostly makeshift system? [As I mentioned in Shougun's thread, I think "Tamer" has its place as a DoL class, with skinning and herding being additional parts of it.]
The same goes with Ninja. Is a Ninja really incapable of using a sword, an axe, a bow, or does he just use those weapons under a different combat focus than their base users?
Our liberal English-translated class titles already fit the most open-ended way to convey how the base classes function. It doesn't feel weird that a Marauder may carry a Fire spell with him, or a Lancer a Cure. And even more so with the original Japanese "spearman", "bowmen", "swordsman", "axeman", etc, there's a lot of ground each class can cover in terms of class-stemmed jobs. Luckily, that groundwork is already set. But taken as too strong a rule, or each class as nothing but a weapon and line of abilities meant only to be adapted into a job once in party play, it'll be interesting to see how SE will deal with mixed-stem jobs like Red Mage, Dark Knight, Corsairs, or Blue Mage that all use swords, should such jobs come into play.