XAML doesn't necessarily have strong IDE support, either. Although integrated into VS, it really is no comparison to the "REPL" of HTML/CSS + your favorite text editor and a browser.
Not sure I understand your use of REPL - in Visual Studio you edit XAML in the right pane, and the change is reflected in the left pane as you type. That's more efficient than editing HTML or CSS in a text editor, saving, switching to browser, refreshing page. Can you explain?
That's entirely dependent on your workflow isn't it? I can set up a workspace within dev tools and edit HTML/CSS/JS on the fly and have the changes reflected on disk and on screen without ever losing sight of my work. Add in the networking tools (timelines, profiles etc..) and I have full featured 'IDE' that I can also browse hackernews with.