'The Drop Pod has a transport capacity of 12 models. It can transport a single Dreadnought or Thunderfire Cannon.'
How many models is one Dreadnought? If it can only transport a Dreadnought and nothing else then you seem to be forcing the Techmarine who normally accompanies the Tunderfire Cannon to walk, which everyone agrees is nonsense.
If it is referring to a unit, why can Captain Shrike take a Command Squad when he is not unit name Space Marine Captain?