"...A normal person has a 45% chance of failing to tie a knot? What does that even mean?"
Nice well written text, but I think it distorts the spirit of the rule quoted a bit. It is clearly a rule for tying people up, not for tying simple knots, from the context. I prefer the rule in Xanathar's Guide, but the one in the new PHB is not absurd.
What's Iowa?