I'm developer of Slint and I'm glad to see Slint mentioned.
I want to clarify that we're not trying to mimic the web. We have a great vision for the desktop integration, but we unfortunately have limited resources. Our team is fairly small and we are mainly working with paying customers to pay the bills, which are mostly in embedded space at the moment.
I agree with your points, and while there’s still a lot to do, I hope Slint can become a strong option for building powerful complex desktop applications.
I like Slint, the technical work is extremely impressive. I even contributed to the project! I hope you can realize those goals, you would fill a massive vacuum in the wider ecosystem.