Recently, though, I've become somewhat disillusioned by how it grinds up against significant faults in the d20 system it's built on, in particular the fact that the d20 is only so big of a die and that exponential scaling from size doesn't play well with deity progression.
What you are talking about is inherent to pretty much all game systems, and there isn't a good fix.
Specifically, the sweet spot in a game system tends to be roughly that area in which the PC's bonuses on a task are large enough to somewhat differentiate them from each other, but not so large that either the difference between two PC's bonuses or any one PC's bonus is large in comparison to the range of results permitted by the fortune.
So D20 for example starts to fall apart with the bonuses either get near 20 in size or else the difference between the bonuses of two characters gets close to 20 in size. If you have a +22 to something, then this gets to be a problem. And if you have a +18 in something, and the other person has a +0, then that's also a problem. All of that I gather you understand.
The bad news.... there is no good fix. A couple of false paths you might try:
a) As soon as you said 'division', you've lost your way as a designer. Any mechanic involving division is probably too complex for anything but a video game.
b) You could try using fixed math so that everyone's bonuses in everything continues to go up evenly with the progression in difficulty. But then you run into a problem where the numbers are getting bigger but the gameplay is staying the same so what is the point? See a typical 'Blizzard' Diablo based RPG, including 'World of Warcraft'.
c) You could try rebalancing everything so that now you are playing a new game with a new sweet spot, but you'll lose all granularity prior to this point. Things couldn't interact with each other across scales.
My question is: how do you all handle this in your games - how do you threaten different players with attacks at different times? Surely having only the weakest character or two threatened by enemies while the others are nigh-invulnerable isn't very fun or balanced.
I play for as long as possible in the systems sweet spot, and then when I hit the systems limits I start a new game. Not the answer you want to hear, but one of the more practical ones.
There are actually related unsolvable problems with scale in standard D&D, most easily seen at 1st level. At first level, you have one HD. But D&D has significant problems dealing with the scale of anything smaller than 1HD. Cats, rats, wasps, ants and so forth all have significant and even insurmountable simulation issues owing to the fact that 1 hit point, 1 damage, +1 bonus and so forth are all atomic and indivisible. The smaller the scale the more it becomes impossible to distinguish between things which are, themselves as radically different in scale as the 1st level PC and dragons and whales.
