The problem here is that you are confusing preservation with producing more offspring then the other. You have to pick one or the other as the point of the theory. Preservation occurs when organisms reproduce faster then they die, more or less. Producing more then the other, well that's just a comparison, and doesn't have preservation as a logical consequence but relative populationshare. I think with survival of the fittest you are basically suggesting that variants are negative selective factors to each other, that they encroach on and replace one another, Malthusian Darwinism. Fitness is commonly understood in terms of preservation, reproducing faster then dying, but the meaning in standard Natural Selection is a relative propensity for a populationshare. Fitness and heritability of traits that are uniform in a population is then zero, in standard Natural Selection, because there is no variant to compare to when a trait is uniform in the population.
regards,
Mohammad Nor Syamsu