Optimal for what? I do think the CEO or someone similar needs to figure out what you want from the organization and design it. HR may have input but it is just input.
HR can do the market calibration research. That's a good role for them. Initial fit? That should be the team or team manager. Background checks? Either HR or an administrative assistant somewhere.
Without HR, that work should fall upon the team manager and maybe some assistance somewhere. It can be done though.
Bottom line, yes, there is a role for HR, I think. No, I don't think it is a big role.