Wes,
I don’t know who wrote that but as an LA involved in Design/Build for 27+ years, I agree with most if not all of it.
However, one downside I’ve seen is that a Design/Build-LA/contractor can, after a time, design toward the strengths of their workers and abilities. If they are good and fast at paver installation they may hesitate to install dry-laid bluestone or another material that may be more appropriate for the project. Similarly they may have “x” number of a particular plant available in their yard, well “design them in” on the next job. If a designer can remain true (you define that) to a design and not to what is easiest/most profitable, I think the Design/Build option is of benefit in many cases.