In your explanation, how and where does the massacre of innocents come in?
Like I said, it turned out their target right upstairs was not there, as they'd believed before they killed Paddock and ran upstairs.
The team (probably just 2 guys) needed to get out of the casino:
Which path is more likely to bring success; a highly calm situation in which casino security/LEO's home in on a single armed duo fleeing, or instead one officer atention is completely saturated by the ENTIRE casino (and those surrounding) in total chaos --From which of those two situations would you want to make good your escape..?
So the duo opened fire on the crowd in order to CREAT the chaos that would cover their flight. Hey, those are infidels in a degenerate city, anyway and they were so far away they seemed more like amorphous concepts than people.
It was an area target and they didn't even have to aim.
I don't think Paddock triggered a single round and I don't think he was angry at that casino or any casino. Being a gambler was his cover and his gambling per diem was expensed to Uncle Sugar.