Also, note that evo claims of convergent evolution argue that different and similar forms arise via environmental pressures and so evos already refute ironically the claim that such similarities must be the result of a common ancestor.
Fortunately, scientists know the difference between shared-acquired and shared-derived characterestics.
Take DNA or actually any commonality. There is no reason at all to discount environmental aspects, is there, for these commonalities?
Yes, when there is no common environmental pressure to account for similarities. For example, the radius-ulna arrangement in the forelimbs of tetrapods cannot have arisen in the forelimbs of humans, bats, horses, seals, etc as a result of common adaptation to a common environmental challenge, since they are not used for the same purpose. By employing a sufficiently large number of morphological criteria of a like nature, the chances of a coincident resemblance can be reduced effictively to 0.
In all of recorded history, no science has ever been overturned by an amateur sitting in an armchair declaring that he doesn't understand it. Comparative morphology will be no exception.