Thinking about this some more. It's kind of like the hall of fame--there will always be questions at the periphery, but this is a good standard to use.
It's not 3-4 years. That should put to rest 90% of this "dynasty" nonsense, which seems to start when teams win a Super Bowl followed by a decent regular season.
Truth be told, the Chiefs COULD actually have a dynasty (not saying I see it happening, for all the reasons laid out already), but that this 4-year run is not a bad start to one--4 AFC championship games, 2 Super Bowl appearances, and a Super Bowl victory. If in the next 6 years the Chiefs go to 3 or 4 more championship games and win a couple more Super Bowls, that would be dynasty-like.