Afaik the event design is to break up alliances between Edge Worlds groups and promote them shooting each other. But in terms of roleplay and lore, I can't see why Core and OC wouldn't work together to squeeze Corsairs especially if there is a precedent for their cooperation previously. People say this is the same as Corsairs and Order but I don't think that could be further from the truth. Core is ruthless and will use any means to achieve its objectives. If anything I'm surprised they don't have a bonus on Zoners here.
Back in the day, we used to shoot Outcasts all the time, with the Developers continually suggesting we pursue Outcast-Core diplomacy for the sake of roleplay and adding something to both factions. We simply declined because we wanted PvP activity - and when you looked at it critically, it was mindless! Real ones know. I'd say Core-OC shooting each other was more of a BHG Core thing when the faction was paid to take down high-profile Outcasts by the Houses in Edge Worlds space. When those raids and PvP began to dry up, interactions between the two groups pretty much ceased. So doing diplomacy instead created more interesting roleplay opportunities.
From a Core perspective at least, If Developers really want to worsen Core-Outcast relations best thing is to create a situation where being friends with Outcasts is no longer profitable. They profit more as friends than foes. Otherwise... yeah I don't think this event is that (dare I say bad writing, though I can't really think of a good suggestion myself). The event looks like a really good invitation to hurt the Corsairs where Outcast/Core interests align, which would ultimately be much more beneficial for Core. Maybe in this regard, it was a mistake to add them to the event, but it would be unfair to rip them out now. You can't blame the players for that. Gameplay-wise wise it seems like the numbers fluctuate so that's fine, and if Reavers are involved really it's just a matter of who they get paid more to kill.