No it isn't. Not even close. It's maybe the first cross-platform development "environment" of which millenials are widely aware. But it's only an "environment" in the most ecological sense -- it's a collection of ugly hacks, each building upon the other, with the sort of complexity and incomprehensibility and interdependency of organisms you'd expect to find in a dung heap.

"Last but not least, the web's primitive is a simple page, which is far more useful than an app as a primitive"

For whom, exactly? You're just begging the question.

I'll grant you that "installing" an app is more burdensome for users than browsing to a web page, but the amount of developer time spent (badly) shoe-horning UI development problems (that we solved in the 90s) into the "page" metaphor is mind-boggling. In retrospect, the Java applet approach seems like a missed opportunity.

The proper reaction to something like React, for example, should be shame, not pride. We've finally managed to kludge together something vaguely resembling the UI development platform we had in windows 3, but with less consistency, greater resource consumption, and at the expense of everything that made the web good in the first place. And for what reason? It's not as if these "pages" work as webpages anymore.

A proper "application development environment" for the web would be something that discards the page model entirely, and replaces it with a set of open components that resembles what we've had for decades in the world of desktop application development.