Agree were not experts, we're just a little bit further down the road :)
Also noone will ever be the expert on your child, and your relationship, and your context...
One thing I found useful just as a general thing throughout childhood, is that I firmly believe it's my job to teach ds about emotions. So not to just squish the bad stuff and love the good stuff, but to help him deal with the powerful feelings he has that he has no idea about. Strange to think that feeling angry is just as new to him as what jelly feels like!
I read somewhere that toddlers often scare themselves with the strength of their emotions, as they haven't got a clue what they actually are or how to handle that feeling - or even if they'll ever stop feeling like that when in the middle of a doozy of a tantrum.
I was really struck by that thought and it helped me see myself as the guide to help him through the tantrum, & the tantrum as a force of nature... Not as something that was my fault or his fault, it's inevitable and it's our job to get through it in the most pleasant way possible for both of us. And building the groundwork to make tantrums gradually a bit less likely to happen.
So damage limitation, and calmness, space if my presence was making it worse, and soft reassuring words if he utterly lost it.
That's after the firm no, lifting away, distracting etc. when it's all gone tits up and all reason had left the building.
I think accepting the bad behaviour as just somethkng every kid goes through might help you feel better about it. Think of it not as mortifying proof of your child's awfulness and your failure... But as a natural phenomenon like storms in autumn, or rain in spring. Just a stage of development. You are not in control of storms and rain clouds, you can't stop them so you don't feel responsible if it rains, but what you can do is be prepared to deal with it when it happens - wear a rain coat, bring an umbrella, don't try and have a picnic with storm clouds overhead... That kind of thing, sorry got lost in my metaphor, hope it makes sense :)
Then when he was a bit older I'd make sure I named the emotion he was feeling and sympathized over how rotten it is when we feel like that. And when calm coming up with strategies to deal with feeling angry/ frustrated/ etc.
So now we have 3 things he can choose to do when he's really angry, and I tell him firmly to stop doing x, and give him the choice of what to do, and it works ok at the moment! It's punch a pillow, do angry jumping, or have a lie down by himself in his room.
It was striking how much it helps just to say 'it's ok to feel angry, everyone feels angry' (but it's Not ok to hit out or whatever). So not in any way excusing the behaviour, but recognizing he needed to be shown how to deal with it so gradually hitting (or whatever) wouldn't be the first impulse.
Don't know if that was in Any Way helpful, but for my ds, and me, it really helped take the angst out of slot of situations. Helped me put myself in the role of 'native guide' vs combatant!