I defer to your economic terminology expertise, but Netscape did have 80% of the market during a huge growth phase (people extrapolated exponential growth from a few months or quarters in '95 and '96). What's the term for that position?
Whatever you call it, if Google had that now or very soon, it could indeed ship new stuff and "make it stick". Since it doesn't have that power, I repeat that Dart is fragmenting.
No one is obligated to work on extending existing standards only, not try injecting new ones. Doing both without market power to make the new ones stick is going to make a mess in my view. I keep saying this, do you disagree?
I'm the last person who wants to save JS from extinction. If it were cheap enough to kill, I'd do the deed myself. It's not cheap to kill -- quite the reverse -- and the leaked memo's assertions about it being unfixable are exaggerations at best, and betray a significant conflict within Google.
(BTW I agree there's a smell of "Java-stained ideas polluting [Dart's] design.")
If TC39 had a crack at standardizing Dart or putting ideas from it into ES6, everyone would be better off -- even if Google then launched Dart anyway.
Instead, while we in TC39 were working in the open on ES6 (which is past new-proposal freeze), we knew nothing. That is not just missed opportunity, I call it poor stewardship on Google's part.