Remathilis
Legend
I also like the idea of making an attack stat for this game. But that still does not fix the stat polarity issue.
You will still see str over con, dex over int, and wis over cha (or vice versa). Players cannot naturally place their stats. I want to be smart and quick. Oh crap, now I am overlapping my resources in one area.
Simply breaking the defenses into three stats instead of three pairs of stats has to happen to fix stat polarity. However as pointed out, it makes some stats worse than they already are (INT looking at you). That is why I see this as a core mechanical problem it is not just a quick easy fix. So lets consider options on how to balance the stats more in the rest of the thread.
I noticed your deliberately ignoring secondary effects: dirty pool ole' man.

First off, things that exist in list don't play out well in real life. Lets take an examples.
A rogue's primary is dex. All his at-wills, encounter and dailies are keyed off dex as an attack stat. However, his secondary are Str or Cha; they simply get more boom out of those two scores than say, a wizard. If I'm going for an artful dodger, I can ignore wisdom and max out my charisma. I could also now choose between brutal scoundrel powers (str) or more hp/surges (con). The only dump stat I have now is Int (since it only helps a few skills for me).
Your idea would force me back into my 3e MAD problem; if I want to be charismatic, I need to stat-dump wisdom and thus my will defense suffers. If I want to be a strong melee fighter (like a brutal scoundrel) my fort defense suffers. I don't have the ability points to be strong, hearty, quick, charismatic and wise.
In fact, every class with nearly would get defense-hosed.
Cleric (Str/Wis, Cha) Poor Fort & Reflex Def (though lazer clerics could skip str for con)
Fighter (Str, Con, Dex, Wis) Only class safe. (depending on weapon choice)
Paladin (Str/Cha, Wis) As Cleric (cha clerics could skip str for con)
Ranger (Str/Dex, Wis) Poor Fort defense (archer rangers could skip str for con)
Rogue (Dex, Cha, Str) Poor Fort, Will (see above for skipping str for con)
Warlock (Con/Cha, Int) Poor Reflex & Will (Infernals could skip cha for wis)
Warlord (Str, Int, Cha) All Three suffer! (hosed)
Wizard (Int, Wis, Dex, Con) Ok, they'd be safe too (depending on implement)
Swordmage (Int, Str, Con) Poor Reflex and Will (Shielding swordmages are better off).
Of course, if your combining this with your http://www.enworld.org/forum/genera...-will-class-powers-ruining-my-archetypes.html removal of at-wills, all bets are off and now EVERY class needs uber-stats to remain viable.
Seriously man, just play 3e...