I must admit I like the direction you're going in.
Like you said, I think in Melee, Sakurai was afraid of having a control or speed character(like Fox) with no finishing moves. Now in theory, I agree with him that this is a bad idea, because Fox could run around you all he wants, and chip away at you until you're at 500%, but if he can't finish you then he can't win any matches. Obviously, Meta Knight is living proof that he has changed his mind with Brawl, but we'll have to play more than a 2 minute demo to see if this works in practice. From what I saw, however, Meta Knight didn't seem to have too much trouble racking up the kills, albeit at much higher percentages than Ike and Bowser.
Also(and this was Melee's problem), the Power characters should now be able to live long enough against the speed character's chip damage to get in a few hits of their own. Theoretically, this is all they need in order for the match to be fair. For instance, for every 6 hits a Fox gets in on a Bowser, totalling 50%, Bowser could get 2 hits on said Fox, dealing 40-60%, and it'd be fairly even. In Melee, however, after that Fox got in 6 more hits, he could just kill the Bowser with a Usmash and not give him a chance to retaliate, and since the power characters tended to have horrific recoveries, while the speed and control characters were usually above average, the gap widened even more. Now that everyone seems to recover better, the Power guys should have enough extra time to kill that they'll have a fighting chance.
As to your 3-dimensional Tier theory, I'm absolutely in love with it, because it's a lot more objective than just listing the characters, since that tends to be misleading. Having their actual stats visibly there, if nothing else, is more convenient. For instance, Fox is way higher than Ganon on the Melee tier list, but just looking at it you have no way to know that a good Warlock Punch would send Fox packing. If, as you propose, we see that Ganondorf's power is substantially higher than Fox's, even a total Smash n00b could make this assumption. That was an overly simplified example, but that's all I can think of at the moment.
Anyways, I don't know if your theory will gain much popularity simply because it is a lot more complex than just writing a list of characters, but I'm all for it. Of course, it remains to be seen whether Brawl does play out the way you say it will, since we still don't know how many/which characters made the cut, or how Final Smashes will be integrated into the tournament scene, if at all(another variable to consider on the tier list, I would imagine).
So, I guess what I'm saying is, I like the concept, but we'll have to wait and see. Just my 2 cents.