From what I could learn from that article, the fish are still fish. The data analysis, whether it proves convergence or divergence, is just a tool. The same for the time line regressions. The product of the tool is no better than the assumptions that went into its use. I'll take the article at face value proving that beneficial traits can be enhanced in similar species over some period of time. It is not a rigorous mathematical treatment of the time line because it is dependent on assumptions for initial conditions and regression rates. Choosing the right assumptions, I could use those formulas to prove the fish changed in one week. I don't belive that, but my perfect math would lead to ridiculous conclusions.
That article was discussing merely one facet of the independent evolution of a similar trait--that of being able to generate electricity--that arose independently in two different species of fish. Like millions of other scientific articles, it was focused on one aspect of the evolution of one trait, and was not meant to be an all-inclusive review of the entire evolutionary process that led to the existence of the two fish species being discussed. Of course those fish are still fish. My purpose in linking that article was to give a small idea of how much the science of evolution--whether one is considering the evolution of a single trait, or the evolution of an entire population--is dependent on the discipline of mathematics. That particular paper depended heavily on statistics. Others use different mathematics disciplines to analyze their data. In any case, I was rebutting the claim that evolution science is somehow divorced from mathematics, which it is not.
That post which I was rebutting also made another error that I did not correct, which is that mathematics is a pure science. It isn't: mathematics is the method we use to try to describe the physical world in terms humans can understand. Physics, not math, is the basis of all science.