Maybe once the core onError lifecycle is implemented (if maintainers decide to go that way) everyone will discover you're right and an implementation will be built in. I think that's probably what's going to happen. But until real life has proved it, it's usually best to go for the smallest most broadly applicable solution. I can definitely imagine <svelte:error> eventually being a thing, but it's a pretty dramatic change compared to an added importable function.

There is no use learning the word for “aardvark” in Swahili if you are never likely to use it. Think of words you use all the time and get familiar with them first.[2] X Research source For example, if you’re an exchange student in Russia, you might need to introduce yourself, ask for directions, and order food. While you might need to know the Swahili word for “aardvark” someday, you can learn it at a later date when the time comes.