Rarity isnt directly based on level. There are green and pink rarity items as low as like level 15. It is more related to the source of the item typically.

And a crafted HQ item will be 10% better on advanced stats(str, vit, crit, etc) but not on damage or defense values. The damage and defense numbers wont be quite that big of a jump.

Ok, those questions were both kinda answered already, so i mainly posted to answer your crafting question. Here goes. Crafting is definitely relevant. The current crafting tier allows making gear of ilvl 250. The newest tomestone(scripture) is exchangeable for ilvl 260 gear, and completing the hardest content in the game currently rewards ilvl 270 stuff. But you need to remember that you can only earn a limited number of the current tome per week, so it takes awhile to get a full set of gear that way. And you dont just start doing the hardest content with a fresh level 60 and the roughly ilvl 145 gear they would have. You need to upgrade to even enter the savage scene. This doesnt automatically mean crafting - there are other methods of getting your gear up to par. They just take time and effort or gil(you know, if you decide to just buy a set of 250s someone else crafted). In addition, crafting is an excellent way to gear up a new class you may decide you want to level later on. And it isnt just gear, there are other things crafters make that people still need at high levels. Every raider wants good food and potions to get the extra advantage on their opponents too. So... no, crafters arent redundant.