You could also just remove the stat bonus from attack+defense calculations.
It's generally still wise to have a high primary stat due for damage - but replacing replacing the stat component makes a few other things easier too, oh, like dealing with weapon expertise.
Rather than have 0.5*level + stat modifer, have something like +0.75*level +3 instead (or, if you will, start at +3, rise by +1 on every level except multiples of 4 plus 1, i.e. 1,5,9,13,17,21,25,29), and ban weapon/implement expertises and the epic defenses feats, and remove the masterwork component from armors (masterwork components which add something other than AC could be reintroduced but would need to be rebalanced). Racial stat bonuses should still affect attacks and defenses, but that's simple to calculate.
For added diversity, you could mandate that your primary stat's associated defense gets a +1, while your non-associated stat takes a -2 or so.
This system would involve less complex calculations than the current system (fewer factors involved) but retain stats for subtler things like damage and skill bonuses.