Obviously under the current hotseat conditions a turtle would have no chance. Battles have to be auto-calc'd, ergo city walls and towers are meaningless. So even if you start with the same quantity and quality of troops your blitzer opponent has, his generate income by sacking while yours bleed it away sitting about the fort. There's no contest and no question IMHO. By turn ten his armies will be three to five times the size of yours even if you're much, much better at managing cities.

Even granting the turtle expands as fast as the blitzer, he's still going to defend his provinces (That's the definition of a turtle, after all) while the blitzer brings those troops to the battle at a time and place of his choosing. It's the modern warfare 'revolution' all over again, speed and mobility vs static defenses. The turtle loses.

Even granting them everything equal, the blitzer will bring more troops to the table and fight them when and where he chooses. As long as battles must be auto-calc'd the turtle is dead meat.