Small question: Are the 10 websites thematically different or do they cover the same topic? I personally usually would keep them seperated. "Never change a run

Small question: Are the 10 websites thematically different or do they cover the same topic? I personally usually would keep them seperated. "Never change a running system". Every time you move a project and 301 all subpages that is a potential risk. Google might currently weight the authority of the domain much higher because you have merged all projects together, but nobody can guarantee that it'll be the same in future. In my ~14 years of seo experience I've built the most sustainable projects by simply trying to think of if something makes sense from a user's perspective. (But I must say that I'm not as active in seo as I used to be) Anyway, the most profitable projects weren't necessarily those which were the most sustainable.