Ok, ok. Here's some arguments then. This is getting really silly.
First, I would like to note that due to Firn saying Sabrina will basically act how the thread acts, she's going to have a massive panic attack and internal argument about how to deal with Kyuubey.
Incoming Gendo Mami.
Systemically, yes, however that does not preclude him not trying to fuck us over in particular. For instance he has made no particular effort to screw over Mami even though he easily could at any point.
True... He wants Sabrina to witch only
as badly as any other meguca. He stays with Mami because she's a useful tool, a powerful magical girl who attracts others to become like her, while still totally in the dark about the true horror of the system. She's good cover, so he can play the stereotypical magical animal/familiar. She's lonely, so she seeks out girls to contract. And she's brittle, as a bonus. The second after she helps bring down Sayaka's witch it's murder-suicide time. Mami is not an example of incubator fair play.
He wanted Kyouko to come in and push her buttons with Sayaka's JUSTICE so she's not a good example either. And with Madoka he said outright "let me know if you're up for becoming the worst witch in the world to help me out kthksbai."
Being hostile to Kyuubey is not rational until he makes some particular effort to screw us over, before that it's entirely possible for him to be not obstructive. For him to be helpful and give us intel.
He'll be exactly as helpful as he needs to be to meet his own goals, no more no less. What possible intel are you hoping for that's worth Kyubey knowing the Sabrina knows things she shouldn't? And also, how would you phrase those questions in such a way as to not reveal metaknowledge?
Homura has shot Kyuubey for stress relief. If anyone other than Walpurgis was her enemy in the loops it was Kyuubey. Homura does not like Kyuubey. We have no reason to believe this sort of thing stopped just because Homura told Kyuubey about someone no one could remember when she thought he couldn't do anything about it.
Homura shot Kyubey to keep Madoka from contracting. She was chill enough with coobs to hang out with him and let him ride around on her post-Madokami. She told him a story that was backed up by nothing about a girl who never existed retroactively, and coobie sealed her soul gem as a trap so that he could conduct experiments on Madoka to make energy collection more efficient.
Yes, you're not taking Rebellion as evidence. But the fact remains that the incubators pre- and post-Madokami did not change one bit. They still seek energy to prevent entropy, they still contract little girls to fight horrible monsters. The monsters changed, the system did not. The end result of the system, the witch consequence for the meguca and everything after that, was taken by Madoka's wish, but that's all. Even using just the series as evidence.
TL;DR: Coobie a shit, avoid if possible, deal with sparingly and great care if not. He is on his own side.