WPF is fine as is and doesn't need to be changed. Generally people who complain about this think that str builds are overpowered, which really shows how much they don't understand the underlying mechanics of this game. They often just quote percentages instead of applying real-world calculations.
When it comes to damage, the two most important things are initial weapon damage and damage type. They are FAR more important than PS. A build with high PS does not do tons more damage than a build with low PS.
As an example, I made a few different builds and punched them into this damage calculator.
http://alpha-lider19.ru/MB/ I like to use this calculator for these examples as I find this calculator to be more accurate.
The three builds are 15/21, 18/18 and 39/3. Each build is wearing no armor and is using a polearm that does 34 blunt damage. Their opponent has 70hp and is wearing 60 armor.
All of these attacks ignore speed bonus and held attack bonus. They are also body shots.
The 15/21 build would kill his opponent in 3-6 hits. That is an average of 4.5 hits which rounds to 5.
The 18/18 build would kill his opponent in 4 hits.
The 39/3 build would kill his opponent in 2.5 hits, which rounds to 3.
With a blunt weapon, the build with 5 ps only needs (on average) 2 more hits to kill the opponent then the guy with 13 ps.
Now if this was conducted with a cut weapon, there would be a much larger difference that would heavily favor the 13 ps.
Strength builds do 2 things in this game: they increase your ability to take hits and they make cut weapons more viable for general use.
Agility builds give you more flexibility and make you harder to hit. You can tear people apart with a 6/33 spear build if you know what you're doing.
WPF in this game is for a few specific purposes:
Ranged Accuracy
Increasing swing speed of slow weapons (WPF affects low weapon speed weapons more than high weapon speed weapons)
Hybrids
If you reduce WPF for non-agility builds, you're just placing a penalty that doesn't need to be there that has the potential to limit build diversity even more. At the end of the day, balanced builds are best anyway. This just seems like a pointless change.