NBC has a ton of influence. I wouldn't pretend to think otherwise. But it's not as if they're sitting in on these meetings telling the IOC what to do. Again, when Australia is deciding to bid for an Olympics, they're not doing it because NBC is telling them when they want it. And it's not as if they're the only organization that prefers that traditional Summer window. So Australia does what they believe is in their best interests to get votes. And none of those votes actually belong to anyone from NBC.
The swimming finals.. again, FINA is making that decision for FINA. They are doing what they feel is in their best interests, not just because NBC wants it. If NBC is so influential, what about gymnastics like they were moved in Beijing (speaking of places were gymnastics has a huge following)? Why not moving the athletics finals? I know NBC asked for it in 2008. And notice how it was 2016 where they started holding finals in the morning sessions, a move specifically for the benefit of European television interests.
I'm not downplaying that American television money is a big deal. But at the end of the day, everyone is in it for themselves - the NOC's, the sport federations, and pretty much everyone else associated with the Olympics. They make self-interested decisions. A lot of times, the decision that's best for them is what's best for NBC.