They’re not advocating for federation at all, but their criticism of the fediverse is based on it supposedly falling short of the “dream” that everyone or at least every technically able person will host their own server:
In the decentralised dream, every user hosts their own server. Every toddler and grandmother is required to become their own system administrator. This dream is an accessibility nightmare, for if advanced technical skills are the price to privacy, all but the technocratic elite are walled off from freedom.
Federation is a compromise. Rather than everyone hosting their own systems, ideally every technically able person would host a system for themselves and for their friends, and everyone’s systems could connect. If I’m technically able, I can host an “instance” not only for myself but also my loved ones around me. In theory, through federation my friends and family could take back their computing from the conglomerates, by trusting me and ceding power to me to cover the burden of their system administration.
None of the federated systems mentioned are dominated by one big player, and I don’t see why we should expect that to be the trend.