Fleet Composition: A fleet can be one or more ships that moves on the campaign map and carries out orders. Up to 33% of your total EP spent on ships may be used to buy ships from the secondary empire. No fleet may have more than 750 points worth of ships. For every ship with Move Cost of 1.0 or greater that is purchased, you must also purchase a ship with Move Cost 0.5 or less. (Not including freighters, etc, it must be a “War ship�). Any Excess MC 1.0+ ships which lose their MC 0.5- escorts can issue no orders except movement towards a friendly base where they will take delivery of replacement escorts. If this does not occur before an evaluation turn (3, 6, 9 etc) the ships missing their escorts must be scrapped. It is a good idea to have some extra escort ships in the fleet. For every three ships in a fleet with MC less than 1.0, you must have a MC 1.0 + ship to lead them. (No building fleets with 15 Frigates, or other silly things like that!) The Overseer has final say in what constitutes a legal fleet. Do not tempt his wrath.
The last 2 sentences are they key.
However, as any reasonable person would conclude that these rules would override any other applicable rule found in SFC for the purpose of the campaign.
Your argument regarding the Orions is irrelevant for 2 reasons: First, they are specifically barred from selection as a race in the campaign; Secondly, the specific option mount allowances listed for each ship in section 5L define clearly what is allowable. You are comparing individual ship limitations to fleets..apples to oranges.
As I look in my Reference rulebook, section 4M does not limit PPD's (nor does the rules update of 12/2009, which is the lates one i can find). If there is a rule somewhere i may have missed, please enlighten me
