Lord Sessadore
Explorer
Seems you forgot that 10 is a +0 mod there. 26 gives you a +8<snip>
At 30 a rogue can hope for about 24-26-28 dexterty depending on epic destiny and starting score. So lets go with the 26 which grants a Dexmod of +13, Leather armor +6 without masterwork qualities is 8 AC plus the 13 dexmod 21 ac from armor and stat Plate Mail +6 is 14 ac... meaning the light armor wearing rogue has 7 more ac from his armor than the fighter without factoring in masterworks
If you go for top of the line masterwork for both in AC pursuits you end up with starleather +6 granting 10 AC + the 13 for 23 ac from armor and stat and the level 6 godplate granting 20, for well 20, that brings the disparity of AC down from 7 to 3. 7 difference is pretty harsh, 3 is at least not too crazy, and that is assuming a starting stat of 18 with a +2 stat epic destiny or a 20 and no stat epic D. Though I imagine most rogues would want to take hide feat to get voidhide and the +2 fort bonus it offers for the same ac as starleather.

So then in the non-masterwork example, the rogue has 8 AC from +6 leather, +8 Dex, which gives him 16 AC from armor and stat. The plate-wearer with +6 plate has, as you said, 14 AC from armor, putting the rogue ahead by 2. The rogue could upgrade to hide for an extra +1 and the plate wearer could add a heavy shield for an extra 2, putting the plate wearer behind by a total of 3.
With masterwork, the rogue has 10AC from +6 starleather, +8 Dex, giving 18 AC from stat and armor. Mr. Plate has +20 AC from +6 godplate, totalling 20 AC from stat and armor. This puts the plate-wearer ahead by 2. If the light armor wearer went with hide instead, they'd only be 1 behind, but the plate wearer can add a heavy shield for an extra 2.
Sorry to pick on your math, but yes, your point still stands. Without masterwork armor, the light armor wearers will outstrip non-Dex or non-Int based defenders. That just doesn't seem right, does it?