It is not a model. Mendellian genetics is science. The fact that Darwin wrote before Mendel changes nothing. He still was wrong and he based his theory on something which has been scientifically proven to be wrong. Genes do not "meld" as they would be required to do according to Darwin. This makes evolution practically impossible.
You have described how you think a mutation, once occurred, might spread in a population. Such an attempt, however poorly conceived, is a model. Yours is a poor one.
I asked you about recessive genes, which I don't see you allowing for.
Two black bears, which have--Tah dah!--black fur, mate. The resulting litter of cubs has one black-furred cub and one cub that is reddish "cinnamon" brown.
What happened there? I don't see your model allowing for it.
Are bears too far from home? Need a human example?
Tsar Nicholas II of Russia and his Tsarina, two non-hemophiliacs, begat Prince Alexei, a hemophiliac. Hemophilia is a hereditary disease. How did that happen?
No, neither Alexei nor the cinammon cub are new mutations.