You seem to think that scientists start with the final premise and work their way backward. It’s not surprising that you believe this, because that’s 100% how religious thinking works.
The fact is that Darwin came up with the idea of evolution because of observations he made in the field: specifically, observations made among similar bird species in the Galapagos, if my memory serves me well.
All the rest of evolutionary theory is based on ongoing observations. The conclusion that you so hate-- speciation going back to the beginnings of life, is an inference-- a rational extension of observations made as we go further and further back in the geologic records and find simpler and simpler life forms. Think of it as kind of a biological Big Bang-- if you follow that explosion back through time, then you can infer that you will arrive at this state.
Saying, “You can’t prove it” doesn’t work unless you have a theory which better matches the available evidence-- which you do not. You have what seems to be a creation myth of early desert-dwellers, supported with a lot of faith but almost no physical evidence of any kind.
So the choice is this: given you believe in the God of those desert-dwellers, how literally should you take their writings about scientific issues like the development of species? My answer-- not at all. Your answer-- completely.
To me the ideal position for Catholics is this: we will earnestly attempt to understand things based on the available evidence. We will accept evolution until actual evidence demonstrates it to be untenable-- just like the rest of the world does. We will keep a faith in God, because God is certainly great enough to guide evolution, and to plan a billion years ahead that this or that lifeform, this or that mutation, and this or that environmental circumstance would lead exactly to me, and to you, and to the placement of every hair on our heads, as He intended.
Not to take this position, in my opinion, is to deny the living reality of God in this world, and instead to adhere in a cult-like way to the limited understanding of ancient tribal peoples. Surely, God’s plan was not to freeze humanity in that state, or to limit humanity’s knowledge to that state; so I see working against science, including evolutionary science, as an act against the real living God who is surely guiding not only the Catholics, but the atheists, the scientists, and every atom in Creation, all the time.