Sugar needs 320 to caramelize, 350 to burn. The darkness comes from a couple things: the already dark ingredients and the smoke sticking to the ribs. The high sugar content doesn't help. Already dark (because it's dark brown sugar), the sugar melts and becomes a sticky mass for the smoke to cling to.
Try a simple re-working, cutting the sugar quantity and switching some to white, upping the quantities of most of the other ingredients, adding a couple 'sweet' spices, and eliminating the irrelevant. For example:
2 tablespoons dark brown sugar
3 tablespoons white sugar
4 tablespoons Aleppo
2 teaspoons black pepper
2 tablespoons granulated garlic (not garlic salt)
4 tablespoons granulated onion
1/2 teaspoon cayenne pepper
2 teaspoons white pepper
1/2 teaspoon ground cumin
1 teaspoon rubbed sage
1/2 teaspoon dried marjoram
1/2 teaspoon allspice
1/4 teaspoon cinnamon
1 teaspoon amchur, if available (optional)
Double all amounts to increase quantity and assemble your ingredients. Place the ribs in front of you. Imagine they are already cooked and were just served to you - unsalted. Sprinkle on kosher salt in the quantity you'd use were you just about to eat these ribs. Flip them and repeat.
Zip outside and start your lit for a Minion start. Return to the kitchen and make the rub. By this time the ribs will be moist from the salt. Good. Apply the rub over the salt. You can use as much or as little as you'd like. Since you've already salted and the rub contains no salt, applying the rub in whatever quantity won't affect the salt level.
I love sauces. I just don't care for the 'meat candy' finish of cooked on sauce, especially when a sweet sauce is further caramelized over a sweet rub, And I prefer the unadulterated texture of the rub and meat's surface, not the thick, sticky cushion of cooked on sauce. YMMV of course.
One way to maintain this texture yet also add the flavor layer possibilities (and shine) of a sauce is to use a glaze at the end. Instead of an opaque Q sauce thickly applied, one instead makes a thick-ish, yet transparent glaze and applies in a thin veneer using a pastry brush, just once or twice near the finish. Something to try if you're interested.