NPC - PvE monsters are currently not in their final form, and will go through a complete revamp before release. I agree wholeheartedly that some are annoying or too strong!
Arena - Arena Masters are already present in game! If they're too difficult to locate, we'll look into moving them somewhere easier to find.
Dun Baldar - We'll see if that's something feasible down the line, but at the moment there are too many other priorities. During Alpha, if you fall, feel free to PM a GM to bring you back up so you can save yourself a footache, they have permission to teleport players for recreational purpose while we're testing.
Weapon Trainer - Thanks for reporting the gnome hunter bug! Adding to the list!