I would use a Red Ranger male over the heritage breed, then only keep the females in the program because that will keep the Rapid Feathering trait. The Males from that crossing would have feathering rate of the mother. If one of them genetics experts corrects me I will gladly submit to their opinion I do not know genetics I only know my own experiences when breeding rapid feathering bird to not rapid feathering birds.
I did not know that Rangers were fast feathering. That would explain what you are seeing.
One sex-linked gene pair controls feathering rate. The slow-feathering gene is dominant over the fast-feathering gene. A hen gives her sex-linked genes to her boys, her girls get nothing from her. A rooster gives one of whatever he has to both boys and girls. So the girls get that gene from their fathers only.
If the hen has the slow feathering gene her boys get it. Since it is dominant that boy will be slow-feathering no matter what he gets from Dad. So the boys can wind up with either two slow feathering genes or one slow and one fast depending on what they get from Dad. It can get confusing if you use that boy in a breeding program, you can't tell by looking of he has one of each or both slow.
A pullet will only get what Dad has. If he is fast-feathering he has two recessive fast genes so the girls will have the fast gene. That's what you are seeing.
I don't know how accurate this chart is. It comes from a sex linked thread on here and is by a guy that is a true genetic expert so probably pretty accurate. It shows some fast feathering breeds and some slow feathering breeds. It's interesting to me that many of the dual purpose breeds we normally look at are slow-feathering. That doesn't totally make sense to me but talking chicken genetics that's not unusual.
Compost King, why is fast feathering important to you? I can think of two possible reasons. Fast feathering chicks will feather out faster so they can handle cooler weather earlier. Hens that are fast feathering will get over the molt faster and return to lay earlier.
If you breed a fast-feathering male over a slow feathering female you can tell the sex of the chicks at hatch by looking at the wing feathers.