Question regarding THF/COR/RNG (noob returning)

[Malithar]

1. Is thf and / or COR in any way a desirable DD end game? assuming they are geared properly?

Geared and played properly, both are capable of respectable numbers. Your DPS will be more of a supplemental nature compared to a main job DD though. The problem with the two jobs are more community based than performance based. Thf is commonly thought of as TH only (though a good deal of recent content does benefit from TH) and Cor has been pushed to the realm of a mules job, except for some of the most devoted players. With that in mind, you may have issues finding groups that take you seriously, or take you at all over someone's mule Thf or Cor.

Cor specifically has taken a backseat lately in the buff department, Geo and Brd are both typically preferred over it, however some of it's luck based JA resets and such are still desired and helpful, if they work, in content. Specifically in Rng setup parties, Cor is very desirable for Courser's Roll though. Both benefit from easily taking a /Dnc sub and benefiting the party through Haste Samba (if your setup even benefits from this) and steps.

2. I know about the recycle trait but as someone who is interested in playing RNG and COR, its seems a bit of a dead end if i want to play using a gun, as ammo is not on the AH? would i have to level ALC to craft my own ammo to even hope to enjoy the jobs end game?

Some of the best ammo is available through other means, specifically plasm, plasm, and sparks ammos. There are some crafted ammos as well, but those are far weaker than the other options.

Crafted ammo here, here, and here. As you noticed, the AH isn't very populated with them. With the sparks bullets beating them, there's not much reason to bother with them, IMO.