If you don't think your leader is fair, you should quit.

No automated system could take into consideration of everything.

For starters, how many times does the player join GNW? Was it qualifier or final?

Then, how much contribution/funddoes the player generate for the gorup, through donation, convoy/plunder and/or SA?

Did the player violate any group rules (this used to be a thing during summon, but with the mechanic change that's no longer so. So there might not be significant rules to enforce now, but it could be a thing)

Perhaps there is some extend of need based distribution, some player who already have all they can reasonably have can opt out. Or player in dire need of new ninja could get them couple times in a row with the understanding (and price) that once they get the one they need, they won't get packs for a long time.

And who knows what else individual groups might come up with.

An automated system that can resolve all those things would require a rather complex setup. Good luck with that.