I have not seen abrasion or nock split on selfbows up to 70#, even using softer woods like hackberry, yew, elm.
I think the nock split problem is more a function of the shape of the string groove than the type of string material. Not sure where the abrasion issue comes from, other than antectdote, or perhaps some dirt or grit got under the string on an example or two. Now I've seen some mild compression on really soft woods, but not abrasion. For yew in particular I would either build up the loops to say 18 or 20 strands (for FF, stuff like 450+ is already pretty fat) or use a harder overly. I have a glass bow (Bobby Lofton, RIP) with an elm overlay, which works perfectly.
I honestly cannot figure out the inherent reluctance to embrace the better material, other than inertia or fear of the unknown. I have never even seen an example of abrasion or split out string grooves, other an 1 or 2 posted on the net over the course of a decade, and of those no indication was given when B50 or FF was used. I wish folks would post pics of their adverse experiences, and the circumstances. I tend to be a pretty vocal and forceful advocate, but it's sincere and based upon lots of positive experiences. I'd hate to be wrong, but would love to be proven wrong.
Until then, I'm going to enjoy the much improved shooting manners, cast and longevity of modern, low-stretch and lower mass material. Actually, since I'm a cheap bastid, I'm gonna continue to use regular old FF, which is cheaper by 1/2 than some of the other premium stuff.
Vintage bows, particularly those from the 70s with no overlays at all, just the glass backing and no string grooves per se, more like string "notches," definately require B50.