Which is what makes this question so perplexing, contradicting testimonials from credible sources.

I've put new new overlays and string grooves on perhaps a dozen glass bows. Some from scratch projects, some rehab jobs. Never used phelonic, only glass and wood, usually wood as the last or top layer.

I have an old Bobby Lofton bow I shortened, piked, and re-tillered. I used elm on top of the existing (looked like .040) clear glass. No worries. Bow is mid 50s at 30", shoots like a house afire compared to typical production mild r/d bows, especially Bobby's run of the mill bows.

As importantly, in my view, I've made dozens of self bows, up to 70#, of woods as soft as yew (althought that bow only 50#) on up as hard as ipe and osage. Rarely use an overlay, even on boo backed, never had a problem.

It can drive a person to madness, because I refuse to take the easy way out by assuming the contradicting antecdotes not credible. But I certainly can't account for the vast differences in experiences.

I tend to fall back upon the theory we aren't really comparing equally in some way, that my experience is subtlly differnent than others. For example I rarely shoot less than 8 grains per pound, rarely shoot over 70#. But I do draw a full 30", and on bows optimized for cast, r/d longbows as short as 60" and use reasonably low mass, low stretch strings, 12 to 14 strand FF, d97, 6 to 8 strand 450+, etc., even linen. And I'm very meticulous about how I design and shape string grooves.

The thing about the flight shooter boys is, they don't mess around about working within the limits of the bow. They run right up to edge of the envelope, and frequently beyond. If they don't know what breaks bows, unlikely yer average 10 gpp hunter, setup with a 400 grain string for "quietness" is gonna stumble on any epithany they haven't already exercised thoroughly. Very uncommon to have an experienced flight shooter scapegoat a string. Rather they tend to accept they've crossed the line in terms of (bow) materials capacity and/or bow design, because their purpose is to use as little string and arrow mass as they can, designing bows accordingly and literally breaking bows occasionally, frequently breaking strings, to find that fine line.

No question a bow string can tear out string grooves. But I don't think you can accurately, fairly, lay all that at the feet of the string material. Rather the size and shape of the string grooves makes all the difference. From an engineering point of view, a chain is only as strong as it's weakest link. Similarly, if you concentrate forces, for example with improperly shaped grooves, stress will exploit that condition... to failure in extreme cases.