I also know how natural selection affects fitness over time in naive simulations, sometimes I get continuous improvement in fitness with no end in sight and sometimes it stops with no chance of improvement in fitness.
Would evolutionists claim that improvement is continuous? Also, what constitutes an improvement depends on the background environment as well as other organisms. Nature may select for local improvements, but changes in background conditions may render such changes to be nonimprovements.
I'm honest enough to say that I have no idea what natural selection would cause over 3 billion years on this earth. Maybe you should admit that you do not know either.
I don't recall claiming to know. Indeed, do people such as Dawkins claim to know?
Natural selection is not so much a theory but a recognition of mortality and its correlation (however weak) with genetics.