This is my thinking too.
My foundation stock are Swedish Flowers, which don't have a standard anyway and evolved on Swedish farms to look and behave as they do. A 6 yr old Swedish Flower (Venka) is mother to 3 pure SFH hens and 1 pure roo (Chirk being the daddy; he is also her son by Sven, which explains why the pullets are so like her - 75% of their genes came from her). The other prominent breed here are Penedesencas, bought in as hatching eggs.
The current dom (Killay) has no Swedish Flower blood at all; his mum was an Araucana (Maria) and his dad a Penedesenca who's since passed (Phoenix). Phoenix didn't live long, but he was a busy and popular chap

, as he has 5 offspring in the current flock, including 2 daughters by that same Swedish Flower hen who produced the 4 young SFHs. There is one certain cross the other way, of a SFH cock (Chirk) over a Penedesenca hen (Polka), and that is Fez. It was hybrid hens' eggs that went into Janeka's clutch, with 1 of her own, so Phoenix's influence continues (probably) in an additional 3 grandkids now, and I'm guessing that the daddy to 3 if not all 4 of their newly hatched kids is the hybrid dom.
The other breeds here have been bit players in the reproduction stakes; Norfolk Grey, Welsummer, Barbezieux, Araucana have just 1 or no surviving offspring.
The upshot is that, after 6 years of existence for this flock, I think that all of the year olds are now related to one another as full, half or quarter siblings or cousins once or twice removed. That the inputs were very different 'breeds' (technically all chickens are the same
breed, we're just dealing with standardised minor variations) I think and hope will continue to avoid genetic depression. It would also be nice if they don't all end up looking like a wall of brown

.