In short With Next you control when things are rendered: SSG/SSR/CSR, so you get much more flexibility and can cover more use-cases. And it is React based, which is a huge plus, especially if you adhere to a modern style.

What use cases does that cover though that Hugo and Jekyll can't? For landing pages and typical business websites for example, some basic ways to create reusable snippets of HTML feel enough for me. I don't want to have to deal with a lot of React, SPA stuff and JavaScript build issues unless it's really worth it.

Next with static rendering (or Gatsby, which I find horribly over complicated) are alternatives to Hugo and Jekyll. If you already know React, they are pretty easy to set up since they handle all the webpack/babel stuff for you, so you shouldn't have Javascript build issues.

When statically rendered, React is mostly just an alternative templating language.