Those conditions would be "Critical", no? The error vs warning distinction doesn't apply.

No, many applications need to be fault tolerant.

Crashing your web stack because one route hit an error is a dumb idea.

And no, calling it a warning is also dumb idea. It is an error.

This article is a navel gazing expedition.

They're kind of right but you can turn any warning into an error and vice versa depending on business needs that outweigh the technical categorisation.