It does seem like LAWA would have a bit of a perverse incentive to suppress traffic at ONT in order to promote LAX, which is part of the region that votes them into office. Inland Empire voters cannot vote for LA City Council members (the bosses of LAWA).
But on the other hand, traffic has been falling at most southern California airports (except LGB, I believe) and indeed at most airports nationwide, so I'm not sure if Ontario is reading this correctly.