I'm not sure what you mean. It presumes that there will be more than one machine. The 'lumpiness' of the universe is likely to produce natural boundaries. It seems to be a small assumption.

It is a major assumption. To use the most obvious issue if someone is starting up an attempted AGI on a single computer (say it is the only machine that has enough power) then this won't happen.

A multi-planetary living system is best described as being multiple agents, IMHO. The unity you suggest would represent relatedness approaching 1 - the ultimate win in terms of altruism and cooperation.

It also won't happen if one isn't having a large variety of machines which are actually engaging in generational copying.

Without copying there's no life. Copying is unavoidable. Variation is practically ineviable too - for instance, local adaptation.

And if the entities lack a distinction between genotype and phenotype (as computer programs unlikely biological entities actually do) then this is also off because one will not be subject to a Darwinian system but rather a pseudo-Lamarckian one which doesn't act the same way.

Computer programs do have the split between heredity and non heritble elements - which is the basic idea here, or it should be.

Darwin believed in cultural evolution: "The survival or preservation of certain favoured words in the struggle for existence is natural selection" - so surely cultural evolution is Darwinian.

Most of the game theory that underlies cooperation applies to both cultural and organic evolution. In particular, reciprocity, kin selection, and reputations apply in both domains.

So your point seems to come down purely to the fact that evolved entities will do this, and a vague hope that people will deliberately do so. This is both not helpful for the fundamental philosophical claim (which doesn't care about what empirically is likely to happen) and is not practically helpful since there's no good reason to think that any machine entities will actually be put into such a situation.

I didn't follow that bit - though I can see that it sounds a bit negative.

Evolution has led to social, technological, intellectual and moral progress. It's conservative to expect these trends to continue.