My argument is that even though there are millions of individuals that don't amount to a hill o'beans when compared to the immense complexities we are talking about.
That is a very vague statement. You have 2-3 billion years of trillions upon trillions of single-celled organisms evolving over the globe, then 1 billion or so years of multicellular organisms. The single-celled prokaryotes are immensely complex themselves, and once brains, nervous systems, muscle systems, and things like that developed they spread across millions of species. "Immense complexities" has no quantitative meaning.
Another problem with evolution by chance changes is that you would have to have innumerable mass extinctions just to evolve one species.
Why? That makes no sense. Nothing in ToE says that one group has to go extinct before another one can dominate. If that were true we wouldn't have the diversity of life we have today, with millions of species all living together on the same planet. And you have to consider chance changes, plus selection, as we keep pointing out.
If there's another guy 1000 miles away he is not going to go extinct just because the other guy can run faster!
Of course not, and ToE makes no such claim.
Even if there are individuals getting different advantages throughout the population it would still take too many generations for the rest to go extinct and for them to dominate because, according to the theory, changes are small and painfully slow.
Why do the rest have to go extinct? There are some 250,000 described species of plants, 12,000 described species of roundworms, 4,000 described species of mammals, and over 350,000 beetle species described. It has never been a situation where one species rises to domination and all the others must go extinct. That is a really strange (and wrong) interpretation of how ToE works.
If evolution is incremental on this small scale it would take forever for the ones with slight advantages to dominate. Many generations. But how long have mammals existed? Only millions of years.
Why do they have to dominate? They can live in different geographical areas, or speciate, etc. Mammals have existed for about 200 million years, with generational cycles lasting from under 1 year to 20-30 years. With a 10 year generational cycle that's 20 million generations of mammals.
The speed of evolutionary change depends on the forcing functions as well as mutation rates. It is well known that exposure to certain chemicals, for example, and cause the DNA repair mechanism to fail allowing far greater mutation rates than normal (ie. more mutations "get through" because the DNA repair mechanism doesn't stop them as it normally would). Drastic environmental changes can cause selection for traits present only in a tiny part of the population, which then very rapidly spread to a new population (eg. bacteria that have resistance an an antibiotic). It is not one fixed rate process based purely on mutation rates, and can happen very slowly or relatively rapidly depending on many external factors (with natural selection operating on the results of any DNA changes).