I have very rarely been able to reverse engineer from an actual product. I started out in UL making my own gear, so have never really purchased much from any manufacturers.
I doubt posting a step by step guide on how to build a MLD Duomid with exact details and measurements would ever hurt the company, because people buy it from them for the high quality that the companies guarantee and to save time. At the same time, I don't think I would ever do this.
I think the difference is the details. I made a mid once with the general dimensions of the Duomid, and it was good. But certain details were hard to copy without seeing the product. For instance, how Ron goes about finishing the peak and vent area cleanly. This proved very difficult for me trying to figure it out on my own. These details are hard to get from pictures posted on the site. And so, I would feel okay posting my pattern and descriptions of how I did it, because the way I did it is very different than Ron's (much better) way of doing it.
As far as detailed how-to's, they have their place. I have written most of my guides in a very detailed way. That was because I wanted to show the little details that I mentioned above. Such as how I went about finishing edges or connecting two difficult pieces. I normally also try to write guides that someone with very little knowledge of sewing can use. Mostly, I write details because I have found the order of sewing the most important part of putting gear together. When I make a new backpack design, I seam rip constantly because I realize that I needed to sew things in a different order, and I when I share a guide with others, I don't want them to have to seam rip ever.
But I can also agree with having an interest in designing. That is probably the part of a project I spend the most time on, and I really enjoy it. And I believe most people who get into MYOG feel that same way. I don't mind starting from someone else's project though. Let's me skip a few boring steps.