Welcome to the Q&A Forum

"My theory is that the uplift generated by the internal linking is subsequently mitigated by other algorithmic factors relating to content quality or site performance or..." I think your initial analysis of the situation is right. Look to improve user-experience, conversion rates and interactions on those pages and try your experiment again. I don't like using bounce rate as a metric for this for several reasons, but if you use Time On Site, Pages Per Visit, or track interactions, such as when they scroll past 50% of the page or click a button... There are plenty of ways to gauge whether your changes are providing a better experience for visitors from search results, which in turn should be roughly the same thing that pleases the algorithm.

So for the pages, would it look like: Blog page 1 "rel next" Blog page 2 "rel prev" & "rel next" and so on?