Hugo is lit. the best platform for static blogs. So why don't I write much more on mine?
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My response to this closing argument in your post about where Hugo "lacks":
> Gutenberg can compile Sass files to generate CSS output.
There is now inbuilt support in Hugo for this for past few weeks.
> Gutenberg will optionally generate an automatic search index; Hugo lacks that feature, but can implement it using several external plugins.
Hugo has a Theme Component feature using using which you can add search to your site using few lines.
> The last feature where Gutenberg pulls ahead is syntax highlighting.
It depends on the language being parsed. The Hugo syntax highlighting using Chroma is super fast and supports syntax highlighting of nested blocks in different languages (again depends on the quality of language lexer which varies with language). So this is not a fair comparison. For example, Hugo highlights #Orgmode syntax which probably no other highlighter does.
Yeah, with Hugo's latest update, the "objective" advantages for Gutenberg are very nearly gone—the two projects are very nearly equivalent.
Subjectively, I strongly prefer Gutenberg's templating syntax, the language it's written in, and the small size of its codebase. But I recognize that all three are maters of taste