"On average all but 2 children must either die or fail to reproduce. Otherwise the species population very quickly goes to zero or infinity."
A population of infinity is of course non-existing. An "infinity" population is not just a mathematical impossibility. What you forget to take into account is that a growing population changes the conditions of the population, and changes selection pressure.
Furthermore you consider evolution of just a single species. But all species are considered to be descendants of the same LUCA (Last Universal Common Ancestor), and there is no mathematical reason to consider each species separately. Or is there? When would you split populations into species and have each their own independent evolutionary progress? Is evolution faster when there are more species? But doesn't the same reasoning count on the number of species: "At equilibrium, each new species means that another species dies out".
The problem is: there is no equilibrium. Equilibrium is a simplified hypothetical state of evolution to make it easy to apply mathematics. As a first step, it is of course a good thing, because it is easy. But drawing conclusions from this simplified situation is a bit too fast. The next step should be to try and find some mathematics that applies to non-equilibrium states. Maybe then you can draw some conclusions about the real world.
"There's a limit on how much complexity an evolution can support against the degenerative pressure of copying errors."
It depends on which level you look. You look at the complexity of each species separately. But why not take each chromosome separately, or each gene, or why not look at ecosystems. The thing is that evolution is not just a thing of species, evolution takes places at all those levels, and what happens at each level, influences what happens on other levels. Again: don't draw conclusions from a simplified model.
So let me be more concrete. Because every model is a simplification. What I mean to say is that the model used here, is far too simple to draw conclusions.
The central statement of this entry is "There's a limit on how much complexity an evolution can support against the degenerative pressure of copying errors".
In order to check the model, the statement should be quantified, so it can be matched with measurements. Maybe something like "the genome of a species can have maximally 50k genes". That requires that the model should be enhanced.
If on purely mathematical grounds was realized that selection pressure can not support 3 billion bases of useful information, before the discovery of junk DNA and the 25k genes in the human genome, then surely there has been some development in the mathematical modeling of evolution since then.