Don't you feel like the leap from a normal encounter to a deadly can take less than a 14 level swing? Aren't you providing an extreme example where another far more reasonable example coudl easily suit?
If it breaks at the extremes, is it rational then to hunt for the point at which it doesn't break and then try to claim it works? If, in order to apply the pacing paradigm, you have to come up with other limitations on both the world and the encounters therein, aren't we then agreeing with my claim?
In other words, I fail to see how finding a milder example that might work explains away where it doesn't.
And didn't [MENTION=48965]Imaro[/MENTION] already address this problem when he said:
These are two ways around there being an impact.
A) The Forest is no longer considered dangerous to PCs once they reach a certain level.
B) If you do want to have a difficult encounter in the forest, you don't need to leap from wyrmlings to ancient greater wyrms....you can simply increase the numbers so it's swarm of low CR creatures, or you can raise the CR slightly and the numbers slightly to achieve the needed math. Neither of which makes the creatures in the forest now capable of threatening kingdoms rather than villages.
A) is a fact of the world, not encounter building, though. If you declare the forest to no longer be dangerous and therefore out of bounds for adventuring, that's building your world to suit.
B) right, which is just moving the pea. Small groups when your low level, huge groups when your higher, why don't they swarm so badly at low level and what's causing them to only travel in huge packs at higher level? Those are questions about the world, and not about the encounter. Answering them requires worldbuilding.
And, further, if you follow the guidance, you should stop counting creatures with CRs well below the player's level in the encounter building math, so, at a certain point, you do outpace many low tier threats as simply not dangerous to you anymore. With a fixed encounter paradigm, this excludes them from being encounters without something actually dangerous on it's own to the players. So, yeah, 400 kobolds might not be a threat to a kingdom, but, according to the guidelines, they're not a threat to a 15th level party, either.