Control: no structured data
The same page shape with no JSON-LD at all. Without this, nothing else here is a comparison.
This page carries no structured data at all. That is the point of it.
Why a control exists
Without a page like this one, every result on this site would be a story rather than a comparison. If a marked-up specimen gets indexed, or gets cited, the obvious question is whether the markup did it or whether any page on this domain would have done the same. The control is how that question gets answered.
What it is
A page of ordinary prose on a subject a person might plausibly search for, written to the same length and the same care as the marked-up specimens, and published on the same day. Same domain, same template, same internal linking. The only difference is the absence of JSON-LD.
Reading the result
If this page performs the same as the marked-up specimens, the markup is doing nothing measurable here. If it performs worse, the difference is the closest thing this setup can give to the effect of the markup by itself. Either answer is worth publishing. The failure case for a lab is not a negative result, it is a result nobody can check.