Build diversity in terms of speccing is usually pointless... everyone ends up speccing the same way else they're considered 'bad'. Blizzard even went and essentially removed the talent trees from WoW because there was no point to them when everyone just used the same cookie-cutter specs. Diversity has to come from fluff and cosmetics really; anything that affects combat will eventually be optimised by the min/max players and the 'choice' becomes redundant.

I try to think of the Jobs as the equivalent of different specs for the classes. ACN is the only class that has more than one spec at the moment but the rest will eventually get them too.