I think semantic HTML and accessibility are massively overlooked — especially because many developers focus on visuals first and structure later.

A lot of people remember metadata and keywords because SEO discussions usually center around rankings, but semantic HTML quietly affects both accessibility and SEO at the same time. Proper heading hierarchy, meaningful landmarks, descriptive buttons, alt text, and accessible navigation all help search engines understand content better.

That said, page speed is becoming impossible to ignore now because performance directly affects user experience and rankings. A beautiful website that loads slowly still loses users fast.

So if I had to rank the most overlooked:

1. Semantic HTML & accessibility
2. Technical performance/page speed
3. Structured metadata

The interesting part is that good frontend engineering usually improves all three together.