No one really disputes that evolution takes place in a smaller time scale within a single species ("microevolution"). The interesting question is whether a species can evolve into a completely different species given enough time.
I’ve seen this debate play out many times. At the end of the day, most people go with their worldview. If you believe the natural world is everything than evolution is likely your best explanation for how we came into being. If you believe there is an intelligent creator than you have more options.
Maybe that's an interesting question, or maybe not. The reason that some people ask this question is that they are predisposed to believe that all of the different species on the planet in the present era were here from the start. This had been the standing assumption throughout most of history, but natural philosophers began to suspect otherwise at least a century before before Darwin came along.
A century or two before Darwin, natural philosophers had begun to earnestly consider the question of whether the present life forms had descended from earlier forms. A major impetus for the debate was that the fossil record had left no doubt as to the fact that the life forms that walked the earth in an earlier era were not at all the same as the life forms walking the planet in the present day. This conclusion had become inescapable, and how was it to be explained, except by supposing that earlier life forms had slowly evolved into the life forms found in the present day? No doubt there were people who proposed that some great cataclysm had occurred that wiped out all the earlier life forms, after which there had been a sort of intervention wherein the life forms found today were newly introduced. But not many natural philosophers would have taken this idea seriously unless there were good evidence for it in the fossil record.
And there were other reasons. Studies of geologic processes indicated that the planet was vastly older than people had previously imagined. The commonality of life forms across the continents was mostly limited to species found on the major northern hemisphere continents. It had become apparent that this commonality was more the exception than the rule, especially when looking at isolated islands in the southern hemisphere, Australia being just one of many examples. Species adapted to extremely cold climates were different for the north pole vs. the south pole. Penguins at the south pole but not at the north pole. Polar bears at the north pole but not at the south pole. A number of similar examples within birds. There were also the embryological studies that suggested that mammals, reptiles and birds shared a common amphibian-like ancestor.
All in all, a century or two before Darwin, there was already a preponderance of reasons for natural philosophers to conclude that the present life forms had evolved from the earlier life forms found in the fossil record. To suggest what you seem to be suggesting (unless you are playing the straw man for reasons of your own), that the process of evolution isn't able to produce new species from earlier species, amounts to saying that the thing that very obviously happened didn't happen. You're saying in essence that because we have no way to prove that random mutations and natural selection can result in entirely new species emerging from established species, that it would be reasonable for us to doubt that evolution can occur beyond the extent of microevolution, and to doubt that present day species had evolved gradually and naturally from the species seen in the earlier era. And yet, there is clearly a preponderance of evidence and reasoning by which no reasonable person can reasonably deny that present day species have in fact evolved gradually and naturally from the species that existed at an earlier time period. Given this preponderance of evidence and reasoning, how would it make good sense for anyone to say that in order for there to be adequate justification to believe that it had happened, that it should first be necessary for someone to prove, in a laboratory experiment of some sort, that it is possible for an existing species to evolve into a completely new species? How would it be reasonable for anyone to insist on proof of this sort, before they would accept the reality of this thing that no reasonable person could deny, because to deny it would be to deny all of the things I briefly mentioned in the two preceding paragraphs? How could any reasonable person deny all of that? The answer is that no reasonable person could.
EDIT: After writing this I realized that you might not be advocating the anti-evolution position but were only mentioning something that you thought worth mentioning. If so, then please don't take this as being directed at you specifically.