What I really want to know is why the Defiant is vaporizing the Falcon in the first place. It isn’t like Starfleet to shoot first and open hailing frequencies later.

I’d expect it to go more like this:

https://www.youtube.com/watch?v=EKJa8lIiWHg

Then either followed by this:

https://www.youtube.com/watch?v=k7jWqD3Zs9Q

Or this:

https://www.youtube.com/watch?v=23vTQDS36dM

…depending on the writers.