I think that he was trying, sure, but he was failing due to his own abusive upbringing. His normal reaction to stress is clearly violence and explosive anger. He's perpetuating the cycle even though he isn't hitting his wife and children - it's still abusive.
He smashed up a shed before in anger. His wife is fearful, but doesn't seem shocked, at his outburst and both she and their daughter are clearly well practised in placating his temper. Jamie immediately accuses Briony of coming after his dad, rather than saying nice things about him (because on some level he knows that he's explosive).
Yes, of course he was under high stress, but the issue is that his stress is displayed and managed through violent outbursts (smashing the shed, chasing and manhandling the teen himself rather than calling the police, wrecking his own van) - it's more of the same, not an exception. That's why they mention the shed in the first place. If they hadn't, then it could have been written off as the stress of the situation. That kind of behaviour goes beyond what is, or should ever be, normal.
His temper, insistence on being "masculine", and the dynamic in the family, is what opens the door to the internet radicalisation, which would have been much less likely if Jamie was comfortable in who he was, didn't see violence as normal, didn't see just rigid gender roles where the women obeyed the men and were subservient as normal, and didn't have an emotionally unavailable father.
It isn't one or the other. It's the combination that is important.