As far as I know the weissman score is for lossless compression and our compression is lossy. But we could compare it to, e.g., x264 running on a single server and calculate a weissman score, but more or less it is then just a speed comparison ;) and in that case we are way faster/better.
You are right on some browsers you need flash as the haven't implemented the MSE yet, but still you get adaptive playback. MPEG-DASH is already working nativly through HTML5 in chrome, ie11 win8, chromecast. Firefox currently implements the support and with HLS together you can reach all major platforms as shown in http://www.bitcodin.com/blog/2015/03/mpeg-dash-device-compat....