The NPC melder doesn't have the same capability as you when melding. They're both worse and potentially much better at melding than you at it. I.e. they can't do advanced melding at all and they aren't restricted by your crafting levels.

The quest is presented as a tutorial about materia in general that just happens to unlock the ability to melds items yourself. This is why I suspect it's required to be able to use the npc melders.

In any event, I wouldn't worry about melding stuff and level 23 since it's definitely not needed and you'll be going through gear really fast. No harm in doing it of course, I just wouldn't stress over it.