I think the thing that’s hard to swallow is how to combine components of both the explanations you gave. And other info is the perp searching other concert venues, and that no “spur of the moment massacre” would occur at the last song of a 3 day festival.
Sum Ting Wong but what???
I think Paddock was there to continue in selling arms to these muzzie baddies, continuing to gather info on their ring/cell, in the hopes his superiors would later roll up the whole ring, pump them for intel, or less likely, flip them via some type of blackmail.
These guys came to this particular meet at this time and place with the intent not of buying, but of ripping him off, then doing the hit upstairs.
Some allege there were photos showing a Saudi Prince getting armed federal protection:
I think the reason why the feds were in town was not so much to protect this Prince (various royalty plays in Vegas all the time) but to stand-by in case something went awry with this planned arms buy.
I don’t think Paddock was witting to the whole Saudi Prince/upstairs angle, in his mind this was going to be just another transaction with the Bad Guys.
I think the bad guys’ latest info, which they acted on, was that the Prince really was upstairs:
Whoops.
I think our gummint plans to NEVER tell what this was really about and after the public memory of this has sufficiently dimmed they’ll pump the “disgruntled gambler” angle a whole lot, then close the fetid book on it.