I mean, as far as Scholar goes that changes a bit as time goes on. Each job plays a bit differently even if they can perform the same role. You can't just play one the same as the other and expect it to work. White Mage, as you pointed out, is very reactive, and has lots of big heals. Scholar is more proactive with the shields and such.

With regards to the proposal given you said that it's fine if they're new jobs what you're basically asking is that they double the number of jobs currently in existence. As neat as that might be hypothetically it isn't a practical request. I also feel like you'd want a third non-DPS role so every job could be a DPS/something else, and divide it a bit more evenly. But that's an aside as the core part, doubling up the number of jobs, isn't reasonable.