I haven't used DART yet, so I will not comment on the strength or the weakness of it
But, all through the decades that I've been in the scene, there have been so many programming languages invented, but so few of them being used
Some of the more widely used programming languages like C, for instance, are not perfect, but they are being used partly because of legacy, partly because of momentum, and partly because of the laziness of programmers to learn new, more useful languages
Talking about legacy, the other day there was a piece on Cobol, and that IBM is trying to extend Cobol to the cloudsphere
As for the languages that are not so-widely used, some of them are downright weird, but then, there are gems among them. The only downside for those few gems is that the ecology is not there to enable those few gems to become more widespread
I guess it's kinda Darwinian game plan --- not all surviving/thriving species are perfect, and not all the extinct species are bad, either