Well based on the powers of logic, if agility can't be buffed anymore, then strength needs to be adjusted.
From a shielders point of view, agility builds are not viable. Anything less than ps6 is worthless for almost any weapon (with the exception of military picks, but 1 weapon doesn't balance an entire class) and I have many times with my mighty iberian mace hit an unhelmeted character in the head only to watch them survive.
Mighty Iberian mace, PS6, shot to the head and survive.
Maybe for 2h weapons the damage is viable with 5 powerstrike, but like I said before for shielders the only viable builds are either strength heavy, balanced, and all the builds in between. With the changes to the heirlooms, the amount of damage added before made a 15st-21agi shielder build viable, now its not. Even with ps6 and mighty iberian or my mw italian against a strength build it takes between 4-8 hits to kill them, when it only requires 1-2 from them. No matter how EZ mode blocking is with a shield, its still really hard to hit someone 4-8x more then they hit you, with faster/longer reaching weapons.
If increasing damage on lower amounts of PS and decreasing damage on higher PS, it would make agility more appealing, which is exactly what we see here in this thread.