I have to say that is one of the more reasonable and lucid answers I've seen from a Darwinist. I respect your belief, even if I don't agree with it, so I will give my reasons.
Sigh, again, Darwinist is an asinine term.
No one is a Darwinist.
The very fact of sexual reproduction creating imperfect, but functional, copies of individual species means that each individual will have changes from its parents. Could such accumulated changes lead to a useful adaptation? It could if it were random; random changes can bring about any random result. But it is not possible if it were only possible if guided by natural selection. Why?
Because for natural selection to be the explanation for say, a bat having wings unlike it's mouse-like ancestor, not only must it's wings be more useful for survival and/or reproduction than the mouse-like front legs, but each and every step in the transition from front legs to wings would have to have added to each individual's survival and/or reproduction. Not just a little bit, but significantly enough that the descendants of all individuals who did not have that genetic change dies off while the descendants of the animal with the first tiny step from front leg to wing thrive and take over the niche.
The results of each and every one of the hundreds, if not thousands, or tens of thousands of genetic changes needed to go from front leg to wing must each have had that effect. But we know that most genetic changes either add nothing to survival/reproduction, or subtract from it.
That most changes of consequence are negative is an assertion that you have not backed up. The fact that history is littered with FAR MORE dead ends in the evolutionary past than exist today should tell you that even if the vast majority of changes were negative it would be irrelevant anyway. It only takes a small population to survive for evolution to take place. No one said it was a kind process. Another thing that points to evolution as the sheer brutality that exists in nature is blatantly evident.
It is true that each step had a survival advantage as well for a transition however it does not need to be a large one. Virtually any survival advantage will propagate when isolated and within a small population.
And, indeed, we do find each and every step in the thousands and thousands of transitory forms. We even find those steps today. Virtually each and every single step in the formation of eyes, for example, exist in one or multiple species today as the eye has evolved several times. We can track how that development happens in those multiple steps.
Further, those multiple evolutionary paths show how they were evolved along separate lines as they do not share common design. There are a limited number of options for eyes so they evolve in the same manner but show distinct differences based on the exact way the particular feature evolved. Indeed there are key differences in each of them that shows they were evolved separately alone separate paths.
Dawkins liked to point out the pharyngeal nerve as a clear cut example of this as its rout is nonsensical if it was formed originally in any of the mammal body plans. It does, however, make perfect sense when you take into account that changes need to happen in tiny increments.
It is also worth noting that, while more species have died than currently exist, the diversity of life is far more prevalent now than has been in the past. The further you go back, the narrower life's diversity gets. That was is one of the problems with the 'orchard' of life example, that is simply not possible on that model. ALL forms of life would have had to start at the beginning and that has been shown to be false in no uncertain terms.
I know what you will say here: that given a sufficient amount of time, so many changes are possible. That is the real answer to the question of what Darwinists have faith in: the passage of time. I call it the Kamala Harris Theory.
Call it what you want, the age of the earth has been established in a dozen ways.
Again, evolution is better attested than almost any theory. Do you also doubt gravity?