What follows is a simple but powerful argument. Because I'm borrowing ideas from other fields of study, the parallels are not 100% but with almost any measure of comity you should see how they align.
In 4e, you pick a class and have limited opportunities to diverge from that class. For the sake of the hypothetical, lets say you pick fighter. When a new fighter option is added, it creates many new potential fighter builds. If the new option was a fighter 4 power, every build of fighter 4 and beyond now has the option to use that power.
In 3e, you pick a class but can easily multiclass into other classes. If a similar "fighter 4" option is added, it creates many new potential builds for any build that has four levels of fighter. There are substantially more 3e builds with fighter 4 than there are 4e builds with fighter 4. An analogy would be to say that when you add an option to 4e, the additional option expands the game linearly. When you add an option to 3e, the additional option expands the game exponentially.
In other words:
- 4e. Number of builds = (number of options)
- 3e. Number of builds = (number of options)^2
- Ensure all builds are balanced
- Lower transaction costs to move between builds
Third edition relied more heavily on the second route to balance by making multiclassing easy. At first it strikes against intuition but grows obvious the more you think about it--the lower the transaction cost to acquire any power, the less important balance becomes. If a 3e class were created with a level 1 power of "Gain +10 attack," everyone would take it and the game would remain in balance. Sure, it would be stupid and distract players from more interesting powers, but it wouldn't actually break the balance because everyone could get it.
The problem with 3e, though, was that each class progressed linearly. The deeper you go into a linear path, the higher the transaction cost to get there. If we change the hypothetical to a class with a level 4 power of "Gain +10 attack," now the balance is broken. In a party of 8th level PCs, the first player to restart will mop the floor with his companions and soon everyone will want to die to get those critical 4 levels. You'll see that it would be even more dire if it were an 8th level power that granted "Gain +10 attack."
Now consider that the exponentially increasing builds of 3e relied on linearly increasing high level powers. An added Fighter 4 power must be weighed against all builds that do not have Fighter 4, which is many. A Fighter 12 power must be weighed against all builds that do not have Fighter 12, which is the vast majority. The same issue that plagues 4e plagues 3e, just later in the game.
This system (which I'm tentatively now referring to as Runeward) takes the lessons from the above and goes a step further. By arranging powers not linearly, but by class score (a composite of character level and class level), you expand the number of builds to which a power is available. In fact, to an 8th level character, no power (save a capstone power) is more than two levels removed from any build. What this means is that the transaction costs between builds are extremely low and there are a great many builds.
In other words:
- Runeward. Number of builds = 2^(Number of options)