'I'm going to kill you' is a common expression, surely. People must live in a parallel universe to me if they think this is in some way usual or only said in abusive relationships.
I don't think anyone has said that? I agree that in the right context it can be perfectly jovial. I don't think anyone would say it's indicative of abuse in and of itself (though it's a bloody horrible phrase in reality).
People are seeing it in the context of him having admitted to anger issues, displaying what looks like very controlling body language in multiple videos, shoving her in what looks like anger, generally speaking to/about her with an expression of absolute fury, and repeatedly saying things like that when she's not responding in a way that suggests she's ok with it. It's the picture as a whole that doesn't look good from the outside.
As a celebrity part of his job is to think about how he comes across to the public. If they're just very talented actors and this is all in good fun, then fine, but they should be thinking about how what they're doing is going to be taken and the implications of normalising behaviour like elbowing, slapping, and threatening. Frankly, they shouldn't be too confused that people are calling it out. It's a weird joke which is far too easily misinterpreted, and evidently not going to endear him to his target audiences. It's unpleasant but probably a good thing he's getting a wake up call if only for his business interests. Make a happy family apology, people forget, everyone moves on, he makes a few more million because he's suddenly relevant and family friendly again before Christmas.
If it's not an act, and this is an indicator of underlying issues, then he's been called out and that's not a bad thing either. Plenty of women will see it and realise that actually, they will be believed if they come forward.