I will check out your link, but this argument is bogus on the face of it. The results might vary from species to species, but the principle of uniformity would demand that the process be the same for all species. And, given the time frame involved with the Celocanth, it seems that the Theory of Evolution would have to explain why some species are not seen to evolve.
Sorry, I checked out your link and I don't see any serious refutation of the Celocanth observation. (But to be fair, your link points to a pretty elementary and cartoonish discussion of evolution).
Natural selection is testable in the lab among viral amd bacterial strains as well as other species.
It is speciation that is not testable.
You said:
"there may be enough genetic change"
This is the kind of assertion that is unsatisfactory to scientists such as myself. I would put such a statement in the same category of speculation as a so-called intelligent design claim.
The post you responded to referred to phenotypes. You don't know that there is any significant genetic change in the Coelcanth from the Devonian. But you posit that there could be because you believe in speciation, the nontestable part of evolution. That is circular reasoning.
Then you cut to natural selection which ***is*** testable under the same species. The Coelcanth and the Devonian may be phenoypically different internally or in some small exterior measure, and they may be genetically "shifted" although not in a statistically significant sense. There may be enough similarities to categorize them in the same species. In fact, the probability is that they are the same species.
So the original poster's question stands unanswered.
Here's a recasting of the question: if natural selection coupled with mutation is what drives evolutionary speciation, why has this 'fish' remained unchanged over millions of years. Why has it not crawled out of the water as a penguin or some other species by which to validate or perpetuate the evolution 'story'?
It is the inductive inference in evolution theory from natural selection to speciation that is the culprit of doubters. And don't think that scientists accept or even respect that inference because it is flawed, terribly so. And in not respecting it, it does not follow that one then must believe in so-called intelligent design.
Belief systems are collections of opinions amalgamated on weaving some core idea to explain observations. Astrology is one example as is intelligent design. And parts of evolution theory (e.g. speciation, common ancestral assumptions, etc.) properly belong in the realm of speculation in the same sense as intelligent design.