Why?

I agree. Whenever I read 'rock-solid' my distrust alarm goes off and it's almost always reading some buzzword laden marketing text.

Because it expresses the authors confidence but doesn't give anything informative. Show me metrics, features, idioms and working examples.

Meanwhile, you can download and try the sample code. https://github.com/sveltejs

I spent a few days testing and it was an eye opener, compare to the numbers of >100 outstanding issues filed in React, Angular, etc which may probably never fix it for some reason and complexity.

Something tells me, should svelt get to the number of stars that React and Angular have, you'll see a similar number of issues.

At a minimum, it's a bad comparison metric. It's like with any software rewrite: the first 80% is the easy part. It's when you get down to the fine details of handling specific edge cases that things get really complicated. (Seeing this in a rewrite I've been working on myself.)

Semi-similarly, there's three reasons why React (and other libs) have that many issues: they've been around for a while, they're very popular, and the wide variety of usages has led to a number of edge cases being found. Svelte, being new, hasn't run into any of those things yet. Things like style of development can also affect things - some communities might file more issues than others.

We need a robust testing system to reduce bugs, improve performance and do some recommendation where code quality can be simplify or better security. I believe not many community can affordable the time to write testing, even expertise skived and problem appear at compile time.