For anyone interested, I've found that the AI values in gen 6 seem to 
work in the same way as gen 3. That is, they are represented by a bit field, 
where only the first 8 bits (starting from the LSB) are used for story 
trainers (it's likely that the Maison has its own set of AI scripts, 
just like the Battle Frontiers did, which makes it favour certain very 
specific moves). Each bit represents a certain script for the AI that makes it 
behave differently when set.

While I can't say for sure, the following settings seem to be correct based
on some loose tests in game:

00000000 (0): Very dumb. Will use moves completely at random, much like
wild Pokémon.

00000001 (1): Dumb, but will at least not use moves that your Pokémon is
immune to unless it has no other choice, or your Pokémon's ability grants
it an immunity (the AI never seems to figure these out).

00000011 (3): Somewhat less dumb. Not sure exactly what it does.

00000101 (5): Used by the Rivals for most of the game (they upgrade to 7
for Victory Road onwards)

00000111 (7): As high as it goes in the Story, at least for single battles.
Should go for super effective attacks and has a high chance to use
stat changing moves when it can't 2HKO your Pokémon. Seems to be glitched
in that it will almost always use Solar Beam if it is sunny, even if
another move will do more damage.
 
10000001 (129): Dumb, for Double Battles.

10000111 (135): Best AI for Double Battles. Also seems to work for Triple
and Rotation Battles, don't know if it's actually needed for those though.

Credit to knizz and daniilS over at pokecommunity for researching the 
gen 3/Fire Red AI, which this is largely based on.