Good update leading to a nice cliffhanger, but I was a little puzzled by this.
AFIAK explosive shells using gunpowder started to be used in OTL by the Chinese in the 13th century. They were in use in Europe by 16th or 17th centuries. I was under the impression that Rhomania was as or more advanced, so would expect cast iron shells with gunpowder fillings for sieges. I don't think they were used for field battles because of the difficulties of getting the fuze timing right (no impact fuzes, just cloth impregnated with gunpowder that could not be timed precisely). Shells that don't explode near enemy troops are useless, but those that explode inside a besieged city or fort will do some damage even if they explode several minutes after impact.
Maybe Doukas' army was not fully equipped for a siege and did not have shells?
en.wikipedia.org