I am a cis man who could not grow a full beard until I was past 30 years old. As you say, just a matter of genetics.
I remember mentioning that to a young trans guy friend of mine a few months ago when he was just getting started on T.
He was surprised, thinking pretty much all cis men have full beards or at least can grow full beards.
I think he felt better about his slow-ish transition knowing that.