If you mean "everything but HTML-based web sites", that's accurate. If you mean the actual Web sites, I really don't see it. The Web is huge, so isn't exactly dying, but it certainly isn't winning.
Native mobile is "winning", in terms of being usually a far superior UX, and by sheer numerical demand. Native still often (thankfully) uses architectural elements of the web (URIs and HTTP) and the UX of Hyperlinking. But the HTML web as we know it hasn't kept up well with the native experience. With the massive investments in IoT being laid down along with VR/AR experiences coming out of Facebook, Google, and Microsoft, this trend will likely only continue, unless someone releases a new innovative hypermedia format & client that catches on.
"They're giving you new languages and development environments because they are holding on for dear life, and I'm not willing to accept being charmed into closed development environments."
I applaud your commitment to openness, truly, but I suggest you need to look at the global market little harder. These companies are not holding on for dear life. They're growing in power. I watched the WWDC Keynote. The crowd just about had kittens when they announced Swift will be open sourced. Twitter nearly exploded. These are anecdotes yes, but the numbers are backing Swift's meteoric rise.
Apple has a vested interest to promote Swift far and wide, perhaps even going so far as Sun did with Java, with the hindsight of their mistakes. Whereas Google could have done this with Golang but seem to be keeping a lid on it for unknown reasons. Best theory I have is that Apple is a product company and Google is a technology company. Golang is making good headway as a server-side language mainly by several companies that aren't Google.