I don't understand. Do you mean two independent state owned companies? That makes no sense, so I assume that's not what you mean! What's the difference between privatisation and having two independent companies?
Consider broadband Infraco and Telkom. Both state owned, so why did government not just give Telkom the old Transnet and Eskom fibre? Why create Infraco?
Telkom sells products that compete throughout the whole value chain. They have historically been anti-competetive when it comes to open access and would likely charge high rates on the national fibre so as to not leave much margin for people competing with their higher level services.
Likewise any independant generating company will be in direct competition with Eskom yet have to sell their power to Eskom. This is a complete conflict of interest and a risk to any prospective power generator.