Mostly people are talking about second classes, which may or may not be getting supplied with crafted gear by themselves or FC buddies. For your first class there's a lot of roadblocks in terms of main scenario progression that really slow things down a lot, and if you're doing a lot of sidequests for the storyline that slows you down as well. Plus on second classes you get a 50% XP bonus for being lower than your highest-levelled combat class.

In terms of levelling crafting skills, it's not really worthwhile trying to keep them up as you level - unless you're going to level all the craft skills at once (which will be expensive and take up loads of time) there's so much interdependency between craft skills that it's not really practical. It's much easier to wait until you're high level with a lot of gil saved up and and just spam the hell out of crafting leves. However, it's still good to do mining and botany, as the daily provisioning quests for your Grand Company are quick and easy, and a great source of seals and XP.