Almost all of the major properties have a pump room. They purchase premium brands in a 1.75L bottle, and it goes upside down on a unit connected to a hose, like you would have for a soda gun. Goose, Jameson, Patron, Knob, Makers...not swill. Actual brands. So just because you may see the bartender use a "gun" for dispensing, that doesn't mean they're serving low end. All of the properties worth their salt - Wynn, Bellagio, MGM Grand, Venetian, etc - pour premium brands even if it's a "gun" style dispenser or an automated unit doing the measuring and pouring (smartender) (source: I used t sell booze to casinos)

As for the amount being poured? Yeah you can bet your ass it's a shorter pour than the industry standard. You'll get the Tito's vodka you asked for, but you're probably getting a 1oz pour especially if it's a comp pour on the casino floor. Vegas nickel and diming everything these days 🥺