Strong control over the math implies (to me) that they are again looking to balance the game at the encounter level, rather than across an entire day (or an entire adventure).
Mathematical game balance can only be achieved at the encounter level. Because in order to be able to come up with metrics you can "balance" you need to be able to know the resources available to the players when they come into an encounter. The more variable the possible resources they have as they enter the encounter, the harder it is going to be to reliably determine encounter balance.
In 3e they thought they could balance encounters across the entire day and came up with the whole CR measure to do it. They were wrong - CR never worked the way it was supposed to for a whole lot of reasons. In 4e they moved to have player resources be somewhat predictable per encounter rather than per day and that worked - you could actually balance encounters in 4e mathematically (and once you fixed the damage and hp math for monsters, the combats were even exciting).
But people didn't like it, so for 5e they've gone back to the AD&D approach to balance - handwave it and count on DMs to figure out how to make it work. They threw in some encounter balancing tables as a nod to 3e fans expecting that guidance, but imo they're as related to encounter balance as using HD to determine threat danger in AD&D was - a good rule of thumb as a starting point, but don't be surprised if it actually turns out to be a tpk or a cakewalk.
I suspect that the PF dev's are still in the place where they think they can achieve mathematical balance. But they still have a lot of per day resources in ther, so I'm curious to see how the encounter building part goes over the long term. If they figured out how to crack that nut I'll be impressed.