There are a number of reasons that I made it expert. One There is a glaring lack of stealth archetype expert classes. If you want to play a stealthy expert class you can play the Shinobi if you want to use Miracles (though it does have a non-miracle build as well) you can play the mist dancer if you want to use arcane magic and you can enjoy a nice bout of crying yourself to sleep if you want to play a sneak expert class without magic. The source idea was a 4E Paragon path (I don't think I used a single ability from it but that's where the core concept came from.)
You're not wrong. There aren't really any 'sneaky' Expert classes, but that might be because we've got so many sneaky base classes. Burglar is the finest example of a d20 sneaker I've ever seen, really.
Honestly though, the big one is I feel like this fits an Expert class more than a master class. This is a class I would play as an expert class but not as a master class, I feel like Battleplanning and those feats/sneak die are core to the concept and really say "guild thief" as where without those, there's nothing really built into the class to say "In charge" or "Sneaky." Besides, I already have a Master Class Thief in the Master Thief.
I've got a couple of nitpicks there... For example, the Burglar and even the Assassin only get a die of sneak attack as a pick-one, at Level 6. Crafty seems to view Sneak Attack as something done by the scout or by feats. If you're wanting to make a big, master guild thief, I don't think Sneak Attack is really the way to go.
Let me put some ideas where my mouth is:
I would drop the mandatory Sneak Attack dice entirely. Just make the C into solid, pure bonus Covert or Terrain feats. There are tons of Covert feats that grant sneak attack, so if that's what someone wants to do, let them. In addition, I'd drop Battle Planning (since these guys aren't going into battle), and replace the D with the following: Heist Planning I
: At Level 4, at the beginning of each scene, you may choose a roll for each teammate to take on and gain a +2 Moral Bonus with the associated skill. Each teammate may only take on one roll. The Brains
: Tactics The Face
: Bluff The Inside Man
: Blend The Mask
: Sneak The Muscle
: Athletics The Safecracker
: Prestidigitation The Sly
Stealth The Tough
Whenever you assist an ally of a check where you granted a bonus to the associated skill, both the threat range and your assist bonus increase by one.
That desperately needs a wording fix from someone, but it rolls in the concept of your A, gives you a new, unique effect for the class, and really plays up the idea that this guy is the master planner of their group, ready to take care of things and capable of slipping in anywhere.
What this has encouraged me to do, however, is find a better name.
I totally approve of that.