I actually think they balance encounters around even lower than that. World first clears have parses that are gray by today's standards. Which makes sense, honestly.

It's important to keep in mind that the average level of play is what encounters are expected to be cleared at. With that in mind, balance only truly matters insofar as it makes the game either too easy or too difficult, which is something that just does not happen at this point in time. There are other factors that the devs likely take into account, such as when imbalance causes elitist casuals to exclude jobs from PF, or when it makes people wonder why they bother playing a job they otherwise enjoy the gameplay and aesthetic of. But ultimately, this game has always been designed around clearing content, not competing at the highest levels. And designing around both is both incredibly difficult and not ideal unless you tune encounters so tightly that the two are more or less one and the same. And before you say that's a good thing, consider that even Ultimates aren't designed like this, and they take around five to ten times longer to prog than an entire Savage tier. Balancing around the highest of the high end would and has been shown to kill the game's raiding scene.

That's why I think it's perfectly okay for jobs with mega-cursed optimizations to be too strong as long as the average level isn't that far ahead- to design around potential would literally damage the game. And I say this as someone who generally prefers playing the most damaging jobs and competing for the highest numbers.

And I honestly think you'd have to take encounters completely out of the equation to think otherwise, which I think a lot of statistics-oriented players sometimes do.