Your last sentence kind of makes the rest of your paragraph impossible, doesn't it? "Realistic" = attacker gets seriously injured. Act otherwise and to the untrained eye, it's going to look like it's not "realistic", like they''re "just falling over" or "jumping". There's no getting around that, so why try? Do you think having the attacker scowl and grimace and bellow is going to make it more convincing? Why not have them throw a few gang signs while you're at it?
There's no valid reason why the attacks in these demonstrations and videos could not be more realistic. In terms of the excessively co-operative uke, perhaps some middle ground needs to be reached between resisting the technique and excessive co-operation, for the purposes of the demonstration or video. I know the demonstration or video would be less spectacular, but it would be more realistic. When a potential student is contemplating doing a martial art, one of the first things they often do these days is get on the internet and research it, which includes watching these you tube videos.