It's severely lacking in the backend but I guess this is more of a general issue with all so called full stack JS frameworks.
Specifically with SvelteKit the big deal breaker is routing. I also find the whole +page.svelte stuff to be a usability nightmare since I barely use the file explorer to move around a project and instead use fuzzy search. Unfortunately SvelteKit is pretty unflexible so you either love it or hate it.
It's really weird that I agree 100% with all the decisions regarding Svelte itself and how it's evolving (runes etc) but SvelteKit is just a big nope from me.
I wouldn't judge any JS framework like SvelteKit or Next.js on its lacking in the backend. They have a server to handle frontend problems, not solve your backend problems.
Specifically with SvelteKit the big deal breaker is routing. I also find the whole +page.svelte stuff to be a usability nightmare since I barely use the file explorer to move around a project and instead use fuzzy search. Unfortunately SvelteKit is pretty unflexible so you either love it or hate it.
It's really weird that I agree 100% with all the decisions regarding Svelte itself and how it's evolving (runes etc) but SvelteKit is just a big nope from me.