But this belief is only true if the language to describe the structure is html or js which creates not reusable pieces of style/structure.
But when you go for a different approach where everything is functions and strong types (ADT), like when you use haskell for exemple, this debate is over, because you handle EVERYTHING in your code, and stop fragmenting the truth into opaque and dissociated worlds (html, js, css, database, glue, docker, ...).