As a level 100 Gatherer, the fastest way to level IS by going out and gathering. Refining at higher levels, you would need to refine thousands just to go up one level.....Yes thousands! Whereas, if you just go out into the respective zone and gather, you will gain XP respectively. Not to mention, you get gathering buffs (gathering XP, gathering speed) as well as actual character XP/TP in doing so. I believe it requires you to complete a quest first IOT receive buffs (don't remember how I got it). You can also increase your gathering XP/speed/amount by using either pots from NPC (from Phirius Shells) or from Item Shop potions (when sale is available).
As for crafting, you can do as you stated. Let them sit back and use the resources from your gatherer, or.........you can have ALL skills (gather/craft) on ONE SINGLE CHARACTER. In order to do so, you will have to purchase the craftsman scrolls from the Item Shop (when sale is available). Yes, it may cost diamonds, but everything will be on one character. This saves time considering you have to log in/out to gather/craft. If you forget something, relog in/out again....just a pain to some people.
So, there you have it. Various options to consider, but outcome is still the same.