I would say it’s a little bit of both. Yes, there is a slow feathering gene that some breeds have that can be used for sexing just those breeds. And that doesn’t work unless the correct genes are at play.
But I have found with my many backyard mix chicks, that most of the time, cockerels grow their feathers in a certain way and pullets in a different way. Occasionally I have one that feathers out in the opposite category than what it is. So it is no hard and fast rule.
As you have seen, because you have that black cockerel that is feathering in like a pullet, but has the big pink comb and wattles of a male. As far as your chicks that have no tails yet and huge bald shoulder patches, that is classic cockerel feathering. Even though they have no pink combs and wattles yet, watch those ones, because they are most likely (but not 100% necessarily) boys.
Sexing chicks is kind of an art, and even those of us with lots of experience at it occasionally get it wrong. You will know for sure when it either crows or lays an egg. But honestly, you will probably know long before that.