In a very loose sense of the word, every scientific theory is a "guess." But a well-informed guess, which is something very far from a wild shot in the dark. Scientific theories are designed to be explanatory models for the data they purport to explain. Any scientific theory must be testable. It should make predictions. (Neither of these applies to creationism.) If a scientific theory fails to survive such a test, it will be revised, or even disgarged. As long as a theory continues to provide a useful explanatory model, consistent with the data, it will be regarded as a good scientific theory.
You may find these articles helpful. The first is short. The second is much longer, but loaded with information on this issue:
Is Evolution Science?.
29 Evidences: The Scientific Case for Common Descent.
Richard Goldschmidt (Evolution, As Viewed by One Geneticist American Scientist) says, "The incessant repetitionof this unproved claim (of micromutational evolution), glossing lightly over the difficulties, and the assumption of an arrogant attitude toward those who are not easily swayed by fashions of science, are considered to afford scientific proof of the doctrine."
I still contend it takes more faith to believe in evolution than to believe in God. But, if evolutionists were honest about the shortcoming of their religion, maybe there could be more honest dialogue.