Personally, I think Mithril.js is the framework that is easiest to "fully understand" due to the small and logical API. There's no magic or complicated stuff going on if you know JS. The problem with Mithril is that it's not as widely used, so there's not as many resources and a large ecosystem around it.
Svelte.js sort of gives me the same feeling. There's more "magic" in Svelte, but at least its mostly hidden in the compilation step and you're mostly operating in normal HTML/CSS/JS.
Personally, I think Mithril.js is the framework that is easiest to "fully understand" due to the small and logical API. There's no magic or complicated stuff going on if you know JS. The problem with Mithril is that it's not as widely used, so there's not as many resources and a large ecosystem around it.
Svelte.js sort of gives me the same feeling. There's more "magic" in Svelte, but at least its mostly hidden in the compilation step and you're mostly operating in normal HTML/CSS/JS.