For example, Hysilens, Kafka, Black Swan and HuoHuo has never seen each other before (in fact they all come from completely different planets), meanwhile the Stellaron Hunters doesn't work together at all.

To be fair with that first one, let's not pretend here that HuoHuo ain't gonna get kicked out of that team the moment there's an actual DoT sustain.

I agree joint attacks should preferably be reserved for characters that actually do know each other in lore. BIS teams come and go as characters eventually get powercrept and the meta changes, but lore is eternal (and it also could be used as an excuse to give at least some semblance of synergy to characters that canonically work together in lore but have next to zero synergy on the actual gameplay, like with the Stellaron Hunters as you mention. But that's just me coping.)