Flying via ORD or DFW or STL (the latter two only from LGA) should be about the same price as the nonstop, assuming the same inventory is available. The published fares on NYC-LAS allow routing via these cities. They also allow routings via SFO or LAX, but the fare rules disallow their use the 3-class transcons, and of course, there's no SFO-LAS on AA.

I don't see any F fares that allow routing via MIA, so as mentioned above, that would be pricing as JFK-MIA plus MIA-LAS.