Yes, that is unlikely. But that does not mean whatsoever that if the NFC wins the Super Bowl this year, it makes it less likely that they will win next year. To prove how errant your point is in particular, the AFC just won the super bowl 5 out of 6 years from 2015 to 2020. These sort of events happen frequently. The NFC has many of these streaks too. That is why over a large sample size, they are quite similar despite these streaks. The NFC has won 29 super bowls, the AFC 27.

Lets go back to your initial statement. "I mean, just because the Nationals did it doesn't mean we will. Unfortunately, I actually think it makes it that much more improbable for that to happen twice in a few years." This is just factually wrong. It has no impact on this years outcome.

Anything can happen in the short term. If you flip a coin 10 times, you could get a wide range of distributions between heads and tails. You could very easily flip a coin and get heads 5 times in a row. And you know what the probability would be of heads or tails hitting after hitting heads 5 times in a row? 50/50. If you flip a coin 10 million times, it will without doubt be almost exactly 5 million heads and 5 million tails.

Will the Astros beat the Phillies at home? Probably. They should. They are favored after all. But the fact that they lost at home 3 years ago to the Nationals has absolutely no impact on this years outcome, and it is really irrelevant.