I think there's an important difference between this environment and what happened in Vegas. Not to say you couldn't have massive loss of life during a game, but...
-You're not going to get dozens of high-powered rifles into a stadium. Certainly not as easily as in Vegas.
-You're not going to have a quiet, secure place to shoot from either. I think it'd be really hard to get to a "sniper's nest" without being discovered.
-If you're shooting outside of the stadium, there's a lot more cover, and a lot more places for people to run.
Vegas was unique - This guy strolled up to his sniper's nest with all the time in the world to get his stockpile ready. He had the safety of his room to set up. He had targets that were essentially caged in and consolidated. Can you kill a bunch of people in other ways? Sure...but this guy thought this through, and IMO, this was a game changer in terms of how stadium events near high-rise hotels (yes - hotels in particular) will be treated. I agree there are other elevated positions, but not many where the average guy is 1) allowed to go, and 2) he can, without raising suspicion, bring lots of equipment.