[Suicide Junkie]

it takes too long to get a productive planetary space yard even on your first colony and you can not keep up with just one homeworld spaceyards.

You will be able to build full capability spaceyards in orbit of planets, though.
You just can't make them mobile, and you can't build them out in the depths of space...
The homeworld would probably end up with tens of Full-ability spaceyards in orbit.

The reduced ability yards could still be used out on the frontiers to replace automated units and vehicles, build defenses, and repair/retrofit.

Colony ships, and large, crewed vessels could only be built by a planet, or any spaceyard base IN ORBIT of a planet.