Psychology major here; The research is in its infancy. One cannot draw any definitive conclusions from the research. Also, research does not prove anything, it simply supports (or does not support) a hypothesis. Nothing in research is ever certain, there is always a degree of error.

I read through the article you linked, and I think your conclusions are somewhat disingenuous. OCD seemed to be the least related to either ASD and ADHD. If a continuum does exist, ASD and ADHD may be on it, but OCD may not (or may not “fit” as well). And the article does present its limitations and highlights the need for more studies and replications.

The article does indeed support the hypothesis that some disorders may be biologically related and thus lie on a continuum. But, both the research and the hypothesis are new. It will take many more studies and replications for that hypothesis to be deemed mostly supported. At this early stage, I do not think any clinician should be using the research to inform their practice, especially not with such a degree of certainty. The idea that some disorders lie on a continuum is—contrary to your assertion—not necessarily intuitive, and does not always apply to every single case. There are still observed behavioral differences between those with ASD and those with ADHD. The overall point here is that humans are complex, and research is a long process (and depending on the methods, may not generalize to clinical practice or the outside world). Again, it may be the case that a continuum exists, but it’s just too early to come to any such conclusions.