From what I experienced in Hotseat games, I think the advantage will go to the blitzer up to the point that it is a 1v1 match and no other party interfering, otherwise blitzing is a risky strategy if you have not the power (in money and men) to back it up... In the Kingdoms Hotseat that went down the drain, I blitzed all rebel settlements within striking distance and managed to hold up the Jihading armies of Egypt by striking fast in response to aggression...

The only exception to the above would be factions with starting positions such as Scotland and Denmark (with only one challenger at the start)

Moreover, sieges in autocalc are a blitzer's friend as walls are not taken into account and you can get them open with a single siege engine (catapult,...) or after one turn at the most (time to build rams or else)...