One thing to remember is that great changes in the morphology of individuals in a population may take a very long time, assuming that the great transformations are caused by the accumulation of small changes caused by mutations. If we have millions of years, the small mutations may lead to great changes in the morphology of individuals.
If the world is very young, maybe less than 10’000 years, there has not been enough of time for such great changes in morphology. In that sense, the advocates of YEC are logical when they claim that gradual changes cannot explain the differences we see between the diverse organisms. So, the conclusions made by logical thinking depend on how old the Earth and life is.
I do not support YEC and from that background, the claims of the advocates of YEC do not seem to stand critical scrutiny. At the same time, I recognize that the conclusions made by the supporters of YEC are logical if their basic assumptions are valid. Scientific evidence does not give any support for the claim of a young Earth, which makes the conclusions based on this assumption false.
Edit:
If we have a population that experiences a beneficial mutation once in a decade, there will happen 100’000 such mutations within a million year. If the rate of such mutations is once in a century, it still means 10’000 such mutations within a million year. If each of these beneficial mutations gives a small advantage to the novel (mutated) individuals, leading to the increase of these novel types within a population, there will happen a gradual transformation of the offspring, compared to the original population. 100’000 beneficial changes (steps in transformation) is much and may lead to quite big changes in the morphology of the individuals, at least if the surrounding environment is changing. It is very probable that the surrounding environment will change within a million years. In addition, some individuals are likely to travel to other type of environments during this period. Their offspring will look different after a million years.