I don't think it is an issue of "scientific" versus "unscientific"
It's really an issue that many UX designers don't know how browser rendering works, so they design static pages as if they were printing in a magazine.
Pixel perfect mocks are terrible for designing responsive UIs. Trying to build pixel perfect pages in a browser is impossible. Somehow these designers get through school with zero understanding that designing for web is different from designing for print.
It's 2023, I don't think that's really the case any more. If anything, designing for print is now the part of the discipline that has to suffer through "web-isms".
The reality is just that designers gonna design - and designing is often an unscientific craft, pursuing aesthetic values before practical considerations. Google and Apple designers are well-paid and experienced web-heads, and still they led us into a land of well-padded desperation.
It's 2023 and I am still explaining how responsive design works to new design grads that my company just hired so there's definitely some failure somewhere.
It's really an issue that many UX designers don't know how browser rendering works, so they design static pages as if they were printing in a magazine.
Pixel perfect mocks are terrible for designing responsive UIs. Trying to build pixel perfect pages in a browser is impossible. Somehow these designers get through school with zero understanding that designing for web is different from designing for print.