I took a look around that site. Scrolled through 25ish pages of the forum, looked through most of the article topics. Nothing. No relevant postings on this topic were obviously available. Or maybe i missed it. Being a site dedicated to everything oil i'm sure they're on there somewhere, but after coming up dry on a topic that I think would be discussed a lot on an oil forum I gave up. If there is a search field or button anywhere on that site then it's not available to non-members. I'd like to read whatever articles or threads you read that have made you so certain that "That's just not true". You shared your experience and used the word "Myth" so perhaps i'm not seeing it but you didn't offer much evidence that it's not.
Now, as for my take on that? It's simple. It's "That's your experience". I know a couple people who have not had problems. And I know several others who have had quite different experiences including myself. It took about 4 changes and putting 20k more on the car to see effects.
Blended oils? That's hardly the point.
Switching back and forth isn't really affecting the engine and its most solid parts. As long as they are lubricated they are good to go. The point is the seals/gaskets in the engine. After thousands of cycles of expansion and contraction caused by the engine heating up and cooling off the seals/gaskets they absorb (even if only trace amounts) some of the additives and moisture of the oils used and grow accustomed to that chemical make up and additives in whatever type of oil you use regardless of it being synthetic, conventional, or a blend.
Its basic knowledge that synthetics use different additives and have a different chemical make up than conventional oils. Switching it back and forth confuses (for lack of a better word) the seals/gaskets and in time almost always leads to some kind of deterioration the seals/gaskets.
Now, getting more on your page. You're not entirely wrong for jumping on the "It's all a myth" bandwagon. For some seals/gaskets it's not as much of an issue. Not all seals/gaskets are made using the same compounds or materials. Some materials resist deterioration better than others. Some materials may never deteriorate enough to cause a problem. And if it does It may take so long that you would most likely blame it on being old. It's certainly not an over night process.
You've obviously researched this subject some too. But I feel you may have stopped a little short. I have done my fair share of research on this in school and in my own time because, like many before me, i was curious if it was really an issue too. After learning about all the different additives and complex sciences that goes into something that the average person likely views as "just oil", I wouldn't consider the chemical engineering that goes into the oils we use and their different effects on various parts to be a "myth".
Summary: Will switching back and forth cause problems? Maybe, maybe not. Does the possibility exist? Yes.