That Youscope thing is pretty cool but then an (analogue) CRO is really just a specialised TV... I would never expect a digital scope to do that good of a job of something like that. 3fps though ain't gonna help. That's where analogue scopes still have it to some extent although newer DSOs are trying to bridge that gap.

We actually had to build a complete video generator (reading an image from RAM using a primitive drawing program) and outputting XY back when I was at uni. Was a good practical.