Hi all, I'm a "totally new" player

I did play the original release (1.0) for a total of 1 day before I decided I hated what shipped, but that is not here nor there. Also got the game a while back but only got started for real last Saturday and having tons of fun, seems the game is indeed a whole different thing this time! However, now I'm extremely confused with the whole class and job structure.

So far, what I understand, it seems that Jobs are an advance class... a Marauder evolves into a Warrior, etc. But it seems the game still gives me some option to keep on playing as the base class... so a Rogue can still be a level 50 rogue with no Ninja and a lvl 50 Marauder can also be a thing.

And here comes my big question: is there a point to this? Is there any advantage, be it solo, or raid, or small group, to playing a base class without a job over the advanced job itself? So far, the bit I seen, the job can do anything the base class can do.