Whether or not a given site should be client-side rendered is a valid discussion
Ad bloat is a valid discussion
Lazy development practices in modern sites/apps are a valid discussion
But in my experience, these as well as other less-legitimate issues all tend to get lumped under the banner of "JavaScript stuff == slow", without any nuance.
Can't say for sure but the way I read them most complaints about Javascript performance are about the results of the abuse of Javascript applications everywhere.
I guess Javascript just happens to be the common thing between a number of them, and people would be just as annoyed if the multi-megabyte, cpu-hogging, data-stealing monstrosities where hand-crafted in assembly ;-)
And: If someone complained about Javascript being slow for scientific calculations I'd probably call them out on it ;-)
Ad bloat is a valid discussion
Lazy development practices in modern sites/apps are a valid discussion
But in my experience, these as well as other less-legitimate issues all tend to get lumped under the banner of "JavaScript stuff == slow", without any nuance.