I respectfully disagree with most of your arguments. I understand that some of the features of the platform frustrate you. Lets start from the beginning.
1 Progressive enhancement) If you think that websites should work progressively even in browsers without javascript, then web components are not for you. I'd say even the older browsers such as IE are not really suitable for web components. Sure, you can use polyfils but that defeats the purpose. So lets get this out of the way, web components are only meant to be used in browsers that natively support them (and also support javascript).
2 CSS in, err... JS) I gotta say I do agree with problems of CSS encapsulation in Shadow DOM. That is why I don't use the Shadow DOM and its the least favorite feature web components to me. Still I don't mind that it is there, and I'm sure it will be useful in some cases. As for having CSS in files that don't have .css extension... you are free to put your CSS wherever you want, you can also put it in you html file. There is nothing in web components preventing you to do it the old-fashioned way. It is just more convenient to develop in a modular way and have code organized a bit differently even if it means <style> strings in your js. Personally, I like it.
3 Platform fatigue) Totally right. It would be much easier for browser developers if no new features are added. It was much easier when we had Adobe Flash. On the other hand, it was Adobe Flash.
4 Polyfills) Also agree (see point 1). Never use polyfills. Web components should be used only on browsers that natively support it. If you are developing a product that needs to work in IE, do not use web components. Period.
5 Composition) This is not really a web component feature. Its just how DOM works. The problem you solved with svelte, you can still solve using custom elements. Also, this is a problem to be solved on a higher level application framework/library. Alternatively, you can make a custom element that solve this problem for you and then reuse it.
6 Confusion between props and attributes) Again, this is not specific to web components. It sucks and I know. It also sucks that attributes are so expensive in general compared to properties. Personally, I developed my framework to rely mostly on properties and ignore attributes by default because in most cases I don't use them. Sometimes I reflect properties to attributes but only as a CSS selector. Almost never do I listen to attribute changes, but in some rare cases I do. Focusing on properties only, helps with this problem a lot.
7 Leaky design) Not a significant issue.
8 The DOM is bad) It is also good. So is CSS.
9 Global namespace) Since you can only register one element of the same name, I think this kind of makes sense.
10 These are all solved problems) If you really believe that, there is no argument to make you think otherwise. I think it comes down to what you think web applications should be capable of. Personally, I think web should one day be able to do everything that native platforms do except: better, faster, more efficient, with better user and developer experience.
A lot of people see web as a platform for static documents with hyperlinks as it once was while others see it as the future of computation. Where on this spectrum are you? According to your writings, I'd guess somewhere in the middle leaning towards former.
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I respectfully disagree with most of your arguments. I understand that some of the features of the platform frustrate you. Lets start from the beginning.
1 Progressive enhancement) If you think that websites should work progressively even in browsers without javascript, then web components are not for you. I'd say even the older browsers such as IE are not really suitable for web components. Sure, you can use polyfils but that defeats the purpose. So lets get this out of the way, web components are only meant to be used in browsers that natively support them (and also support javascript).
2 CSS in, err... JS) I gotta say I do agree with problems of CSS encapsulation in Shadow DOM. That is why I don't use the Shadow DOM and its the least favorite feature web components to me. Still I don't mind that it is there, and I'm sure it will be useful in some cases. As for having CSS in files that don't have .css extension... you are free to put your CSS wherever you want, you can also put it in you html file. There is nothing in web components preventing you to do it the old-fashioned way. It is just more convenient to develop in a modular way and have code organized a bit differently even if it means
<style>strings in your js. Personally, I like it.3 Platform fatigue) Totally right. It would be much easier for browser developers if no new features are added. It was much easier when we had Adobe Flash. On the other hand, it was Adobe Flash.
4 Polyfills) Also agree (see point 1). Never use polyfills. Web components should be used only on browsers that natively support it. If you are developing a product that needs to work in IE, do not use web components. Period.
5 Composition) This is not really a web component feature. Its just how DOM works. The problem you solved with svelte, you can still solve using custom elements. Also, this is a problem to be solved on a higher level application framework/library. Alternatively, you can make a custom element that solve this problem for you and then reuse it.
6 Confusion between props and attributes) Again, this is not specific to web components. It sucks and I know. It also sucks that attributes are so expensive in general compared to properties. Personally, I developed my framework to rely mostly on properties and ignore attributes by default because in most cases I don't use them. Sometimes I reflect properties to attributes but only as a CSS selector. Almost never do I listen to attribute changes, but in some rare cases I do. Focusing on properties only, helps with this problem a lot.
7 Leaky design) Not a significant issue.
8 The DOM is bad) It is also good. So is CSS.
9 Global namespace) Since you can only register one element of the same name, I think this kind of makes sense.
10 These are all solved problems) If you really believe that, there is no argument to make you think otherwise. I think it comes down to what you think web applications should be capable of. Personally, I think web should one day be able to do everything that native platforms do except: better, faster, more efficient, with better user and developer experience.
A lot of people see web as a platform for static documents with hyperlinks as it once was while others see it as the future of computation. Where on this spectrum are you? According to your writings, I'd guess somewhere in the middle leaning towards former.