They aren't in the game.. and even if they were where they were supposed to be (the demonic realm), then you wouldn't have access to them until the final .5 percent of the game.
It really depends on how you want to play the game as to what would or would not be better as a class progression.
ALL of the rogue based classes are more limited than the other available classes.
Considering that the Hatamoto is a dual-weapon melee exclusive class.. AND that you don't want to use Heavy Armor.. then your best 2nd tier 2 class would be:
Celestial.
Reason:
1. it gives you one learning bonus in Rune Magic, which can help you latter in the game with enhancing your weapons and particularly with enhancing your armor magically.
2. it nets you 2 learning bonuses in Celestial Magic, which can allow for some powerful magical attacks via lightening, but more importantly provides you with stronger Blessed Spirits to heal you while you are fighting. It of course also allows you to summon more powerful Divine Spirits.
3. finally, it gives you access to those spells (Blessed Spirits and Divine Spirits) via the Adept route, which you wouldn't have if you didn't take one of your 1st Tier classes as an Adept.
Note that you will still have access to a great many Arcane spells in one way or another, and that you can always buy arcane and nether scrolls (in particular Blast Nova and Blade of Bhaal).
Added BONUS: The Celestial is the only class that has access to the dagger the Diamond Light Crystal, AND its one of the better potential off-hand weapons, (for dual light weapons), in the game as well as being available relatively early in the game (considering its power).
Soul Harvester 
Linear Mode
