The demos of the actual game showcased improvements in recent builds and footages. The platinum demo wasn't even part of the actual game and was made separately. Something that you seem to ignore, still. The e3 demo showed no performance issues but merely a terrible player struggling to find out what the hell he is doing on stage. The stream on the vid linked on this thread isn't exactly a good one which made it look like the game wasn't performing perfectly.
Other streams show a perfectly smooth gameplay footage.
The gameplay here seems wayyyyyyy better than the youtube stream. Like I said before, the guy playing the demo was just plain bad.
Yeah, people should NEVER base their judgements on streams as mostly likely than not, they do not represent the real quality of whatever is being presented. Wait for direct feed footage. However, playing a game terribly can never be masked by any video quality. lol