Not sure if "truth" - more like each situation, but here's my one observation. I have discovered that some dogs have genetically "softer" teeth that wear down abnormally fast with constant chewing/biting toys. Who even thought? That said, Reckless had a jolly ball a puppy and played with it constantly. I mean incessantly, but it was too wild of play to allow indoors so it was an outdoor only toy. Her canines had worn the point off before she was 18 months old. So here are several points: J blamed the jolly ball, which is just rubbery material, very slightly textured. I don't think it was the ball itself, but rather some other factors all coming together - outside where she played was dirt, often muddy from melting snow or summer rains. No lush grass anywhere. So the ball collected dirt/mud/fine sand which stuck to the ball, but dogs don't care about that. But that fine grit would change the surface of what she was mashing her teeth into, right? Also, Dutchies are basically brindle Mals, so obsessed with biting and mouthing, especially as puppies. R would open her jaws as wide as possible, grip what she could and to hold the ball still while she crushed it, she'd push it hard into the ground, re-grip, over and over. Never would carry by the handle. I have seen many photos of Mals and Dutch Shepherds with worn canines and not sure if they are a breed with genetically softer teeth or if they are just so bitey/ball crazy they over-load what the teeth are designed for, which by nature should just be scraping meat off of bones or one hard bite to kill a rabbit. Tennis balls are notorious for wearing teeth with their wirery-woolly surface, so that makes sense. I still am not convinced that a jolly ball surface could do the same damage, especially in a grass/lawn with a dog that chases it and picks it up by the handle and doesn't obsess over "killing it" repeatedly.
All that said, if you got one for Zephyr, and he only carried it by the handle, I doubt it will wear his teeth down. If he grinds it into the dirt, bites repeatedly on the round surface to crush the air out, I'd probably have second thoughts. Is he ball crazy? Obsessed with carrying toys? I wouldn't think his breed makeup would have that trait, but I know so little about guardian breeds. Also, he's not a young puppy and his play might be quieter now.
Also, after the jolly ball was discarded, Reckless's teeth continued to wear down. She playsfetch daily for about 5 - 10 minutes, with no time alone with any balls or anything to chew on, we use those spikey rubber balls so the canines would not be gripping a hard solid surface. Asha doesn't have sharp points anymore, but R's are extremely worn down now at age 10.
There's my Ted Talk.