What I took away from this was that one should be careful with the visual elements one adds, and stop to think about how those additions are helping the primary goal of communicating ideas (this may take the form of reading words, feeling excited about a product, awareness of a brand, or usability of a UI).
I like his example of the screenshots framed by Apple devices (as I've seen on so many websites). Is the goal to communicate that you make Apple devices or that you make content that could work on that type of device? In this case I think (e.g., if this was for a business portfolio showing screenshots of software UIs to potential clients) the goal is more about showcasing the work not the devices; and the more minimalist "flat design" for those device frames would seem more appropriate in communicating the simple idea that "our stuff works on mobile devices".
I think many designers need to keep the OP's points in mind and consider, step by step, why what they're adding to the content in the form of design elements is helping rather than distracting. Do you really need a drop shadow on that image? Does it help make the content's point clearer to make your button look like it's made out of leather? Is that script font you chose for your headings making it easier to read what you're saying? I think these are the sorts of questions the OP wants designers to consider, and I think his points are good to keep in mind.
This deck is interesting and mostly a good way to look at many information presentation situations, but it is another instance of the recurring theme of annoying absolute statements from self-important designers.
There is bad design, there is good design, there is no "proper" design, and any designer who claims so needs to check their ego at the door before you hire them. Design and style evolve, and much of it involves fashion, fad, style, and preference. These elements evolve over time, vary between situations, companies, and products, and are part of the character of the statement design makes.
This presentation would be considered boring in some situations, depressing at others, ultrachic in others.
Not everyone wants to sit on purple glowing cubes with a fernet milkshake under mood lighting in tight pants. Some people enjoy sitting on saddles, twirling their mustaches, and line-dancing the cowshit off their boots.