Well for one I’m pretty sure that DF and second origin aren’t really comparable to begin with and the way you’re interpreting it is even more complicated than the way Urtear explains. I’ll simplify it Mage has one large Jug of juice (Juice being magic power) Juice is used by mage to cast spell.
When spell is cast juice is consumed till no more is left. Urtear power up gives mage another Jug of juice. Mage with 2 Jugs of juice means more casts or larger casts i.e more consumption or larger consumption of Juice without hitting empty as fast as a Mage with one Jug. So no, empty Jugs means you would be useless not stronger. Perhaps you mean one consuming large amounts of juice constantly in training would make your Jug bigger otherwise nothing else fits. Now, I don’t see how DF can be compared to that since the only times it’s activated it doesn’t give more rather it requires a large amount of juice to be consumed, juice that only Natsu can get not from his jug but from outside sources. By the way Natsu never used DF on Hades.