I suspect you misunderstand my argument

Were you claiming that those neural algorithms are thus algorithmically efficient/optimal?

I was assuming that (back in the Cambrian) there were a variety of neural architectures for locomotion "already there".

Ah yes, I didn't know you were assuming that. Unfortunately that doesn't seem very plausible to me. It seems more likely that the locomotion algorithm we see in many species today was a once-in-natural-history luck-out on the part of evolution. Even assuming rival algorithms appeared on the scene, I suspect they did so rarely enough that the first which appeared had such a head start that those which came later could not compete. By simple natural selection, instead of via evolvability. Also likely is that once the first algorithm appeared, it was immediately built upon, such that later algorithms messed other stuff up and cost too much fitness relative to their improvements.

And that the ones that succeeded did so because they had an 'elegant' or 'modular' neural architecture.

Perhaps I did misunderstand you, and you were claiming modularity, but not necessarily internal optimality? But then how would modularity relate to the OP? I guess it is one aspect of being efficient. But weren't we comparing various modules for 'difficulty of replication in computers'?

I have no problem with evolvability in general. In fact it's a favorite of mine :)