So I guess the answer is "things are going to be bad, so why bother optimising?". I guess I can't really argue with a self-fulfilling prophecy like that. Not considering the size of a JS library because the business process is slow? Oh... kay? Just feels like real lowest common denominator stuff: why should I do good work when someone else isn't?

FWIW I did Lighthouse audits on React TodoMVC and Svelte TodoMVC In the performance category React gets 74 while Svelte gets 100.

First contentful paint:

React: 3.8s

Svelte: 0.9s

Time to interactive:

React: 4.8s

Svelte: 0.9s

I can't make you care about this stuff but the numbers are very straightforward.