Saying FFV's job system came from III is a huge stretch. FFIII's system probably has more in common with FFVI in terms of game impact. The classes you chose were meaningless after you switched out of them, and ultimately got replaced by superior versions originally although the remake for the DS changed that a bit. The concept of abilities transfering over and having a use for being a class beyond the immediate was introduced into the FF continuity by V.
Also worth noting that Final Fantasy V was released 3 tears before Tactics Ogre, so really that can never be the right turn of things. If anything Tactics Ogre got the concept from FFV.
Edit: Oh I see you meant Ogre Battle which was released in 93 rather than 92 as with FFV. Clearly the two idea were developed side by side and independent of each other then.
Yeah. Ogre Battle differentiates itself considerably in that classes work almost like skill trees in later games, and the stat growths you get in different classes more easily facilitates switching to (and being effective in) other classes. A Fighter might need 14 Strength and 12 Def to become a Knight, for example, whereas it might need 15 Strength and 10 Def to become a Berserker - and the Knight has better growth in defense than does the Berserker, which means it will be able to switch into the Paladin class faster.
I'm not saying OB doesn't take cues from FF3 or anything, I honestly have no idea on that front.