...but that's what Svelte is not. The techniques you adopt won't transfer over to vanilla HTML/CSS/JS without the magic Svelte compiler. These habits will become crutch when Svelte inevitably goes the way of every Javascript frontend framework.
> something complex like React
React is not that complex, certainly not more so than Svelte. It's hard to wrap your head around some behaviors, but at the end of the day, it is really just Javascript/Typescript. It is programming. As a programmer, I want to spend most of my time programming in a programming language, not so much of it configuring the Rube-Goldberg machine that is HTML/CSS. Your mileage may vary, of course.
> this silly side project made in Svelte over a weekend
I will admit, that's what Svelte excels at.
If your work requires you to use a web stack, this attitude will not serve you well in the long run. If you make the effort to learn these technologies, you'll soon find them to be simple and predictable, but admittedly not without some historical baggage. You may even have an easier time with Svelte, since it has everything working out of the box, unlike React, which requires you to figure out a build toolchain and a separate solution for styling.