Although the OP created it for SSR, these libraries are handy for SPAs as well.

Rendering the whole DOM tree (instead of VDOMs) is a fast process. The slow part is attaching (committing) elements to the doc. e.g., I have a test of 20,000 elements which takes <30ms to render, while attaching them takes 120ms.

Since the performance is mainly bound to the commit phase, libraries like these (and hopefuly a native API) help for creating simple UI frameworks. For example, a helper such as:

  function createElement(tag, props, ...children) {
    const elem = document.createElement(tag)
    for (const [k, v] of Object.entries(props || {}))
           if (k === 'ref')        v.elem = elem
      else if (k === 'style')      Object.assign(elem.style, v)
      else if (k.startsWith('on')) elem.addEventListener(k.slice(2).toLowerCase(), ...[v].flat())
      else if (k in elem)          elem[k] = v
      else                         elem.setAttribute(k, v)
    elem.append(...children.flat().filter(Boolean))
    return elem
  }

    function ResetButton() {
       return (
         r('button', {
           className: CSS.ResetButton,
           onClick: store.reset
         }, 'Reset'))
    }

    function render() {
      document.body.replaceChildren(App())) // but mergeChildren
    }

https://github.com/ericfortis/mockaton/blob/main/src/client/...