The Chiefs had the best offense, but also the worst defense. They lost a playoff game because they lost a coin flip.
You aren't really making a strong case here for 'unfairness'.
We can easily just say: They lost a playoff game because they have the worst defense.
The point does still remain, though, had the Chiefs won the coin toss it is exceedingly likely they'd be in the SB.
The NFL has set up the rules to heavily favor offenses over defenses, so it's kind of just common sense both offenses should get an equal chance.
No it really isn't likely they would have scored a TD and won.
The Rams and Saints both have amazing offenses, the 2nd best and 8th best in the league. But the Rams, the 19th best defense in the league, were able to stop Brees and the vaunted Saints offense.
There is nothing unfair to an entire team in a coin flip. Both teams have a 50% chance to get their offense on the field and score a TD. If you lose the coin flip, go out and play defense, like what happened in the NFC Championship game.