Doesnt campaign have a "gametype" that can be extracted and put into a custom games gametype just like forge was?
No, Campaign uses a 10MB (Save Point) CON File, and it only contains the content of the starting point to be loaded (Usually two or 3 starting points per map).
That has no baring on Forge, or other objects... Ok:
Let's say, Forge uses the map, and then 450 objects to place, so overall it contains 451 things.
Campaign is 1 thing. No objects, it's all BUILT-IN. No Forge in Customs, just Campaign in Customs.