It is time again for teh maths. Again I disagree.
First is hp. It's actually a 14.3% difference. Only 10 hp. Not too much.
No, Balton is definitely right. 70 is 116.67% of 60.
Only 10 hp. Not too much. Depending on the armor you are wearing you'd be able to survive 1 to 2 more hits. With the increase in athletics it's much easier to stay out of range. You're more in danger from team hits than hits from the enemy.
Now let's look at damage because this is much more interesting.
Let's say that each build is using a Knightly Arming Sword. It does 32 damage. With 5PS you'd be doing 44.8 damage per swing. With 7PS you'd be doing 49.92 per swing. However, that doesn't take speed bonus into account. With speed bonus you can do ridiculous amounts of damage. Even with 4PS I can 2 hit some people who are wearing medium helmets with head hits. With a good speed bonus you can meet or exceed the damage of the 7ps. Sure, in a straight up fight if each one was swinging at each other the 15 str guy would go down first, but no fight ever works like that.
Another interesting point to consider. Since armor soak values are also percentage based, the attacks of the 7ps guy would get reduced more than the 5ps guy. Again, helping to bridge the gap. Interesting, no?
What I'm really trying to say is that both of those builds are pretty balanced. Anything that's only 3 points off the norm (18/18) in any direction falls under balanced. Builds that start to go outside of that range start to show the differences between str and agi builds. One big reason is the speed bonus itself. I'm pretty sure speed bonus is capped at 100% giving agi builds a limit on that damage modifier. Also, that same damage modifier works against them. Stacking strength does nothing but good things and the scaling gets REALLY ridiculous with high damage weapons. Agi builds start to get worse as athletics is stacked because you can only get so much of a speed bonus and the diminishing returns of WPF damage bonus starts very early.
Much easier to stay out of range is the same as "Much easier to not be in combat", other than this, 2 athletics isn't going to do shit in a 1v1, it's more about weapon length at that point.
You're either overestimating the amount of difference than 2 athletics makes on a speed bonus or you're not even taking into consideration the speed bonus of the str build.
The soak factor makes less of a difference in how it is implemented, than even a single point in powerstrike would make.
100% speed bonus isn't something you'll see outside of the realm of cavalry and I know, at least in native, it isn't capped at 100%.
I'll finish up my complete damage calculator sometime this week, it calculates damage for all types of weapons(including ranged) then release it to the community. It's from a few months back when the soak value/reduce values were changed the first time, so there's some updating I need to do with it, then run it by Espu/cmp to make sure it's 100% accurate. Everything was taken from cmp's posts/crpg files so there shouldn't be much issue.