I prefer not to project my opinion of what someone else may or may not be doing, but since you have:
My supported professional reason for not completing the cost approach is because I do not think that it is necessary for credible results - something I'd hope you'd not take issue with, but if you do, it in no way affects my opinion.
Where did you get that I believe the form says I can skip it? I've never said that. What I said is that Cert 4 states that I have developed my opinion of the market value of the real property that is the subject of this report based on the sales comparison approach to value.
As an instructor, I certainly would offer my opinion in a classroom environment, but would also welcome - and not judge - those with differing opinions.
And I don't think I've EVER, nor will I EVER, state(d) that I am an 'authoritative' USPAP instructor. Aside from being a poor choice of words (as authoritative can also mean 'commanding'), I'd certainly not consider myself an authority on USPAP. I am, however, an AQB Certified USPAP instructor.