Harness definitely matters more from safety and reliability point of view, but saying that it matters more than Model itself is a slight exaggeration. In the sense that this 'headline' can lead people to believe that all models are equal and Harness can make up for lack of in-built features of a model.
Internal model must have native features like mixture of experts, memory features, etc. for the harness to use.
I recently saw a benchmark of Qwen 3.8 27b in DSH vs Oh My Pi.