I don't know anyone who disputes evolution as Darwin defined it — the emergence of new species via descent with modification and natural selection.
On the other hand, I don't know anybody who has a good theory about how life as we know it arose in the first place. That's where the "complexity of life" issue is the main obstacle to be overcome. DNA and its replication cycle is complex. How that complex molecular machinery ever got started remains a scientific mystery. Perhaps it will solved in this century.
The evidence for Darwin's model is compelling. But it's also important to examine that evidence with a skeptical eye. Some of the evidence trotted out to support Darwin's model isn't probative. That's like including extraneous material in the proof of a mathematical theorem. It's important to appreciate which evidence is probative.
One valid complaint about Darwin's model is that it's a qualitative model rather than a quantitative one. What's needed is a stochastic model that corresponds to Stephen Jay Gould's notion of
Punctuated Equilibrium.
Stanislaw Ulam is one of the few mathematicians to make significant contributions to this important frontier. Ulam's seminal
contributions to theoretical biology should not be overlooked.
And scientists who are concerned about these questions should not be confused with religious fundamentalists who prefer non-scientific explanations for the unanswered questions about the origin and complexity of life.