Imagine a system with only one stat: Effectiveness. Assuming you're doing point buy, all characters will be equal.

Now let's expand it. This system now has two stats: Aspect covers all physical and mental abilities, and Domain covers magic. It's fairly easy at this point to compare two characters, and if one stat is better than the other, presumably all players will build to similarly take advantage of it. There is, however, the chance that specialization causes multiple builds to coexist in the meta. Odds are that these won't be perfectly equal in power - But they should be close, because a system this simple should be easy to balance. Insert "Team-based game" here. As long as all parties contribute a bit of discrepancy is fine, although there's a chance that a less enfranchised player might make a suboptimal build.

Now let's expand the system again. I have the following stats written up: Foot strength, foot flexibility, leg strength, leg flexibility, core strength, core flexibility, arm strength, arm flexibility, neck strength, neck flexibility, jaw strength, jaw flexibility, hand strength, hand flexibility, sight, hearing, tasting, smelling, reaction time, stamina, precision, and insight. In time, I notice that a meta emerges. You see, archers need both arm, hand, and core stats, along with sight, stamina, precision, and insight. Spearmen need every one of those, in addition to both foot stats, both leg stats, and reaction time. Assuming that rolling a high number when using a bow is similarly effective in combat to rolling a high number with a spear, the archers will have a much easier time not having bad relevant stats.

I then add a thief. Thieves need foot flexibility, core stats, arm stats, hand stats, sight, hearing, smelling, reaction time, stamina, precision, and insight. That's a lot, but not as many as spearmen.

Now, let's add mages. they use stamina, precision, insight, and hand flexibility. This is clearly too few stats - mages will break the system in half! So to fix it, I break hand flexibility into hand movement speed, hand contortion, and hand precision. And I break insight into self-awareness, emotional insight, and cosmic truth.

I needed to fix mages using only 4 stats, so I added 4 new ones. Depending on how I design my magic system, mages will need 2 or 3 of them. Archers, meanwhile, go from needing 10 stats to needing 11 (They don't need hand contortion, and use only self-awareness from insight). Spearmen go from needing 15 to needing 16. Thieves go from 14 to 17, needing all hand stats as well as self-awareness and emotional insight, to detect suspicion.

I "Fixed" the problem: The archetype using the fewest stats now uses more of them. The number of stats that is uses grew proportionally more than every other type of character (from 4 to 6 or 7 is a 50% or 75% increase). In numbers, it grew a bit slower or the same rate than the thief, and faster than the archer and the spearman.

But if the problem with my system was that the mage was too powerful, I haven't addressed that, and I've made every other class more miserable than they were before, especially the thief. Thieves might decide that they don't need core strength to lift themselves into windows or emotional insight if they stay out of sight enough. Mages might decide they don't need to cast a few of their giant pile of spells that really need hand contortion, and otherwise their stats are a bit lower than they were before.

Quote Originally Posted by CowardlyPaladin View Post
One of the major design reasons for splitting these stats also balance, the less states you have, the easier it is for certain classes to min/max them, which inevitably helps casters. A wizard really just needs Int and some dex and they are good to go, but the more states around the more damaging min/maxing is, which means anybody who does it is going to be more powerful but also take more of a risk.
Under your system, a few caster 18s may become 16s, as they move from having 1.5 key stats to 2 or 2.5. A skirmisher monk, meanwhile, needs strength, dexterity, adroitness, constitution, wisdom, and spirit. Who's the real loser?

The imbalance in D&D exists at the system level. There aren't stats for recall, for pronunciation, for mental focus, for every minutiae of bending the universe to your will as there are for each step of swinging an axe or having an axe swung at you. You can break stats up and make wizards need multiple, but the atomic units that the system works in are built for wargaming, so you'll need to do a lot of work to prevent other characters from needing those stats as well.

A warlock with all 8s is a playable character, stronger at mid levels than most martial classes. The same is very true of a wizard with all 8s except with the minimum intelligence required to cast appropriately leveled spells. There aren't mechanisms to systemize how the class functions, so they can't be easily balanced by adding stats. You can balance them, but it will be enough work that you might as well not start with D&D as your system base.