I love the "they could have tackled him" argument. Its right up there with tasing. Or "shoot him in the leg."
The tactical decisions can be criticized forever. In hindsight knowing what happened, you can always theorize some alternative outcome had some other course of action been taken.
That has nothing to do with the constitutionality of use of force. That is entirely dependent in this case on whether they reasonably perceived a threat from him when they fired.
And, to boot, when you theorize about what the police could have done differently, don't forget to theorize about what he could have done differently. He could have not walked away and instead cooperated. He could have not reached into the door of the car.
And then, since we are dealing with alternative universes, let's say they tackle him. And then there is a claim they injured him that way. There is uproar over that. Shades of George Floyd on the ground.
In the case of all of this, you have to think in terms of what was known, at the moment of decision. Not what is known later. From another vantage point. And with no information from the video about what happened prior to then.