Addressing this is trivial - add a small amount of randomness. In situations where the AI deems two moves have only a slight difference in outcome, don't always choose the stronger.Basically, one of the big flaws of any AI program is its predictability.
You could add more randomness if your wanted to weaken the AI, but I don't think that's the best way. I reckon an AI on weaker settings ought to play like a weaker human. So do things like discard sets or even whole Pokemon from its database. You could bias it towards not considering recently-developed sets, to simulate a human player who's reasonably good but not 'current'. Or you could give it knowledge of the 'wrong' tier, to be like someone who's good in OU but a novice in Ubers. At a very weak level it might even make mistakes with the type chart. If the AI teambuilds, then at a weak level it builds teams with little synergy and overall strategy, teams just of six strong Pokemon thrown together.
Of course, obi needs to develop the AI first. Then I'd expect his main focus will be on strengthening it, but it's worth taking a look at weakening it. Perhaps one could do a variant on a Turing test - can a battler distinguish a human player from an AI 'set' at the same rating?