"Drowning" is a problem with too much humidity earlier in incubation, such that not enough of the water inside the eggs evaporates through the shell, leaving excess water inside the egg. It really has nothing to do with the humidity outside the egg, other than the fact that drier air pulls more moisture from the egg. That is why "dry incubation" is so successful. The goal is for an egg to lose 13% of it's weight during incubation. I weigh my eggs regularly and adjust the humidity toward the 13% goal. During the most humid times of the year, I used no water until lockdown, later in the fall, I needed to add a little water to keep the RH above 20%. Someone in a very dry area could not use "dry incubation" I guess, but everyone should jack the RH up for hatching, or you will get chicks stuck in the shell that need help to get out (or die there).
High humidity will not directly drown a chick unless water is condensing on the top and dripping onto the eggs, which I've never seen, but you could look out for.
I've hatched hundreds of Silkies (probably more than any other breed) and I wouldn't consider them any harder to hatch than other breeds. Most of them were years ago, when I didn't understand the way RH works, and they still hatched ok, so whatever you do will still likely have some success, I'd just like to see you get as many healthy chicks as possible.
There are variations in hatchability, both from genetic weaknesses and the health of the parents. Show quality strains could be more prone to the genetic issues due to inbreeding for desirable traits.
I believe the 60% RH idea is why your friend needs to help them, and a lack of patience. Some chicks are also too weak to hatch on their own, sometimes due to genetic issues, I think we are hurting our birds to allow those chicks to hatch and perpetuate the problems. Good stock, well cared for, should produce vigorous chicks. I had some hybrids hatching over the summer that seemed to jump out of their shells and compete for who could get food and water first. Commercial hatcheries breed and manage their flocks for that kind of hatching vigor, they would never help a chick to hatch.