How is serendipidy weak?
This feat could just as easily state that you gain a luck reroll and an unconditional +1 bonus to your AC and that would be downright decent but this feat is even better as it effectively lets you trade that bonus for another reroll.
If you take a moment to look around, 99% of all feats that add to your AC provide only a +1 bonus. Improved Natural Armor, Draconic Skin, Dodge, Psionic Dodge, and Shield Specialization make that pretty clear.
While this doesn't stack up against similar aberrant and abyssal heritor feats, it really shouldn't have to. Even if it isn't the strongest of AC-boosting feats, I'd actually say that it's on the high end of the curve compared with the other feats listed above. Add in that the double reroll makes this one of the more powerful luck feats and you have something pretty solid for any luck-based character.