My emphasis is on the word need. I'd happily consider any evidence you've seen.
My emphasis is on the word "risk" (captured in the literal words "most likely"). It's risky to go without a guide, though it's not "needed" in the sense of a 100% failure rate.
Honestly, the fact that you assumed others were talking about "have a guide or 100% failure" is disingenuous on your part.