Well, we'll need to secure their cooperation in some manner in order to permanently break the system, because, powerful as we are, we neither have the resources to break the system in a long lasting way nor the ability to stand up against them should they chose to go against us. Whatever plan we come up with needs to have their approval, otherwise it's only a matter of time before things come crashing down on us.
This is very true. Our wish has not broken the system like Madoka, who's wish achieved her victory in a single strike. Instead we asked for the power to achieve our dream over asking for the dream itself.
Out of all the wishes we could have made, we chose one that is directly useful to Kuubs' profiled desires, the harvesting and extraction of grief. We achieve this by two massively positive goals: Firstly we can directly cultivate large stores of a previously unmanageable resource, and secondly we improve the shelf-life of previously finite wells (Soul Jems). If you think of it in terms of oil drilling, we're a global shipping center, where most girls are individual rigs.
Kuubs faces the challenge of courting a resource that has the potential to massively boost his operations efficiency, but at the same time is MASSIVELY savvy to both his goals and methods. And disapproves furiously. He has to TRY to win us over,
but can't approach us while we're hostile.
The best option for him would be duplicating our powers for industrial use, but that's a separate challenge. If they could just duplicate the effects of wishes, they'd game the system everytime something fortuitous came up.
The end result? We could likely make some rather outrageous demands of him, and he'd likely to comply out of a desire to foster communication at the least, and a better relationship at the best. We should not trust him, or even like him for that matter, but we should not refuse to use him.