I would argue that it is ENTIRELY about design, but the problem is we have a lot of ARTISTS under the DELUSION that they're "designers".

Design is engineering that incorporates art as one of its many aspects. A DESIGNER would know about heading orders, alt text, semantic markup, logical document structure, specifications, accessibility guidelines... It's why a DESIGNER would start with semantic markup, do their actual design in CSS, and so forth; Not sit around spanking their crank on a graphics tablet in Photoshop or other glorified paint programs.

Dicking around with what a page is going to look like before you have content or a reasonable facsimile of future content marked up semantically is utterly and totally back-assward, no matter how much of an industry norm said dumbass practice has been the past 20 years.

We have WAY too many artists CLAIMING to be designers, who are so devoid of the practical engineering knowledge I wouldn't trust them to design a shoelace... much less a website.