Why is everyone so reluctant to admit that no coat can be 100% waterproof? As long as they do their job to your satisfaction, then all good, but 100% waterproof.......sadly impossible!
I’m not sure “every one” is reluctant to accept any practical walking kit is “100 percent waterproof”...force water at high enough pressure against any practical clothing, and some water will get through. But walkers don’t define “waterproof” in that way...a materials scientist might, but walkers don’t.
Reality is that different types of clothes have substantially different degrees of “water resistance”, and in some clothing that resistance is high enough to keep person substantially dry in any conditions likely to be met outside a laboratory.
When we discuss “waterproof clothing”...we are really talking about clothing whose water resistance is high enough to keep us comfortable in conditions we go out in. For some of us..that will be Scottish winters (or even colder and wetter for some)...so there is bound to be a healthy interest in this topic.