One can say it is impossible for someone who has such kind of a history with substance abuse never had a moment where in an extreme state of being out of their minds they got violent and got physical and of course they'd be within reason for saying that as plenty of alcoholics or addicts do resort to that in that state especially in a martial situation.
However I've experienced seeing addicts also at times go in the exact opposite direction where they are in a constant state of self blame and guilt of being addicted to whatever they are addicted to, and whenever they are using, they just don't get into any other confrontation as they are already feeling guilty of putting themselves, and their family (especially kids) through the 'hell' of living with an addict. And having seen that especially in a marital situation what that can do is drive the partner absolute nuts about the situation (not wrongly btw) because they hate seeing someone they love (and in some cases that someone also being the parent of their kids) in that state, and worse not having any will or mental strength to combat that state. So even through good intentions of getting them out of that state (and this is what Amber has said a few times, that a lot of times she 'initiated' anything it was to stop JD from going into another cycle), they end up taking a wrong action that worsens the situation, and that in turn keeps shifting the addict further and further away from coming to their senses as well.
This is just from my experience of course but the kind of evidence and statements we've seen, it doesn't seem too far from it. Having said that, even in that situation the entire confrontational stuff remains between the two people and at no point the partner of the addict would ever go in public to embarrass the one they have had 'good intentions' of helping and bringing them back to sobriety. That's where all that stops for me, and would differentiate Heard from someone genuinely suffering from the consequences of their partner's addiction and only getting in confrontation as a consequence of that to someone who went on to abuse their partner knowing if anything gets out, they will be able to hide everything behind "they were the ones out of their senses, they started every confrontation and I had to always defend myself". That and of course the subsequent lies that have been exposed multiple times (especially financial ones, that's generally where you can see what someone's real intentions are), erase that notion of Heard for me and easily points towards someone who developed ill intentions (even if it was from the mental stress of living with an addict, it doesn't justify it one bit), and went ahead with turning those intentions into confrontations.
Again that's nowhere near saying Depp never got it wrong, his habits have a huge part to play in why the situation got to where it did, and there's no doubt he would have made the situation worse plenty of times. There's no way for us to exactly pin point what his behaviour leaned towards in those confrontations.