If any one stat dominates combat, it will be the overwhelming perk choice. So with a system like this, your perks should either have associated debuffs, or have enemies/tactics/weapons they're weak against.

Trading off strength against agility is a good way to go, especially if both are important in combat. I think you'd also want weapons that favor different approaches more, like for instance a strong character might be best with a greatsword whereas a quick one might prefer a short sword or even a long knife.

The trick is, you want to adjust your battle stats so that the strong and quick characters are evenly matched. If a strong character does twice as much damage, ideally he should also hit half the time, relative to an opponent with a perk.

Armor of course has to be factored into your calculations, and my advice on all issues of stat balancing is to keep your stats low. Like single-digit low.

If you're trying to balance PVP combat across multiple levels and body types, these are some basics that should help:

1) Any training is much better than none, but has diminishing rewards. That is, if you were to think of general combat profieincy as its own stat, it should approach a maximum but never get there. Maybe level 5 is 60% proficient and level 10 is 80%, and 15 is 90%, halving the distance to 100% with every 5 levels but never getting there.

2) HP is traditionally a combat proficiency stat, using high health to basically signify the character's toughness and ability to survive combat rather than literal health. But in most games it does not scale according to (1) above, so it gets all out of proportion. That's why most games with PVP don't balance well with players of disparate levels. Frankly it's more interesting if a level 5 has any kind of a chance against a 15.

3) Like training, some armor is better than no armor. Leather armor will absorb a certain amount of blade damage, although it may be useless on its own against ranged weapons. Any armor will impede movement to some degree, but leather will be closest to natural and will have very very low impact, whereas much stronger armor like plate will have very very high impact on movement.

4) Shields are highly effective if used judiciously. Characters who train to use their armor and/or shields will have better defensive capabilities than those who don't.

The main thing I think is to keep is the logarithmic curve of diminishing returns. A typical RPG often scales levels linearly or exponentially. With linear scaling, a level 50 character is twice as strong as level 25. Exponential, and 50 might be twice as strong as, say, 49 or 45. A logarithmic curve would be very different.

Chances are you'll probably need something that combines linear and logarithmic, so that the user's proficiency can gain quickly early on. One good formula for this sort of thing is a sigmoid.

sig(x) = b^x / (1 + b^x)

A sigmoid curve naturally ranges from 0 to 1, and it has an S shape that stretches out into infinity in either horizontal direction. The exponential base (b) determines the steepness of the curve in the middle.

There's also this law with sigmoids:

sig(-x) = 1 / (1 + b^x)

That's helpful because it means we can make the calculation faster by only doing exponentiation once.

For something like combat proficiency the way I would envision it, let's say that stat goes from 0 to 1 (1 being 100%). Then you'll want something like sig(x)*2-1, where x is your level. So imagine level 1 starts at 5% combat proficiency.

sig(1)*2-1 = 0.05
sig(1)*2 = 1.05
sig(1) = 0.525
b / (b+1) = 0.525
b = 0.525(b+1)
b = 0.525b + 0.525
0.475b = 0.525
b = 21/19

So you could create this formula:



Exploring that formula a little more, if level 1 is 5% proficient, we can get combat stats for the other levels:

1 0.05
2 0.099751
3 0.149007
4 0.197536

To get to 50% proficiency:

sig(x)*2-1 = 0.5
sig(x)*2 = 1.5
sig(x) = 0.75
b^x / (1 + b^x) = 0.75
b^x = 0.75(1 + b^x)
0.25b^x = 0.75
b^x = 3
x = ln(3)/ln(b)
x = ln(3)/ln(21/19)
x = 10.977

So you'll just pass 50% proficiency at level 11.

The general formula, if you want to figure out which level x gets to proficiency p:

sig(x)*2-1 = p
sig(x) = (p+1)/2
b^x / (1 + b^x) = (p+1)/2
2b^x = (p+1)(1 + b^x)
(1-p)b^x = p+1
b^x = (1+p)/(1-p)
x = [ln(1+p) - ln(1-p)] / ln(b)

Obviously this is just a suggested system and there are many other choices, but that math should help you decide if the numbers work out the way you like.