The hardness of a stone has very little to do with its susceptibity to breakage. Diamonds are the hardest known stones but they split easily when struck parallel to a crystal face. Most glass is harder than steel -- try scratching some with a knife -- but it breaks easily. Jadeite is quite soft (fairly easily scratched) but it's the toughest of all stones because it has an interlocking fibrous structure. That made it the ax material of choice by early human toolmakers.
Quartz family materials like chalcedony, jasper, agate, flint, chert etc. share the property of conchoidal (shell-like) fracture, as does obsidian (volcanic glass). That makes them very suitable for controlled flaking into arrowheads and spear points. It also makes it highly unlikely a pristine example like the spearpoint in question would survive undamaged and relatively unweathered for thousands of years.
There's always the possibility the point was buried deeply and was found before rough stream action could damage it. I hope so. But I'm skeptical.
I do understand what you’re saying and bow to your expertise. I do know though that what we find has survived for thousands of years in some cases (I think) around a spring that is used by range cattle. It seems that some are unearthed by wind or rain or perhaps the cattle overturning rocks and dirt that amaze me in their condition.
That said, I’m strictly amateur at this.