I think what that person meant was if browser default styles made semantic HTML look more beautiful, it would probably reduce the incentive for lazy devs to make div soup.

Like imagine if every browser preloaded a dozen attractive classless CSS frameworks for users and/or devs to choose from sort of like CSS Zen Garden.

If all browsers had that, I think we'd get less div soup.

Three things I think:

(1) Unstyled HTML looks terrible.

(2) There's relatively few native components and the ones that exist are limited. Like not even what JQueryUI gave you 15 years ago limited. No cards, accordions, avatars, and other sorts of basic building blocks.

(3) No real support for common page layouts. Like a Dashboard or Hero marketing page sorts of things.