If you have a messy codebase with logic mimicked on both the back and front end its not just the developer experience that suffers - the user experience will eventually suffer too.

I mean isn't that what ruby on rails is? RoR's minimum response time is WAY slower than most other frameworks. Getting a ruby on rails page rendering in under 100ms is work, while other frameworks getting it under 50ms isn't much effort at all.

Tradeoffs everywhere. If I needed to serve my pages to an area where downloading 1mb would take a minute and that was my core demographic, I will be making very different choices in tech than what most people have to write for.