<-- when dungeon / raid gear is better ?

Im a new player, levelling as Arcanist and wanting to be a Summoner / Blackmage later in the game.

I was talking with the guild, and they said that dungeon / raid gear is better than crafting gear.

So let me ask here, why would i level for example Weaver - when other gear is better?

Is there anything else you would recommend me level for a new player, something that can help/is good for me?