You can use Svelte completely separate from SvelteKit - we've been using it for a while now and integrating with our pre-existing APIs with no issues, some of those are serverless, and some are just instances behind a load balancer.
You can, but that is obviously not a happy path the svelte devs want you to use. 90%+ of tutorials and docs out there are for doing things with sveltekit.
I eventually beat it into shape of generating a true SPA, generating paths that weren't at the root of the domain, and I convinced express to serve up assets accordingly. Took way too many days to get it working though.
