Piracy should be either about scooping something really rare 4 or 5 units - or getting something en masse which is desired relatively high.
As for balancing against current passenger exploits - which I expect will be gone in Q1 - that's not how game design works, that's not how to balance things against.
I also don't expect piracy to earn same level as legit earning. However, FD should look for fun and challenging ways that well rewarded to extend piracy gameplay. What we have seen in Q1 seems to give some interesting raiding gameplay which might be finally something new for those looking not only pirate measly traders.
Oh, nothing is going to balance against the current passenger missions. But there are plenty of legal ways with non-exploitative stuff to earn 30-50MCr an hour. Trading can earn 15-20MCr/hour in reasonably common circumstances, probably quite a bit more. Mining can earn over 30MCr/hour if done optimally (and that's *before* Beyond's improvements to it). Piracy is like those two basically about obtaining cargo and selling it ... and in absolutely favourable circumstances which are more glorified mining than piracy (an unshielded harmless NPC T-9 in an Anarchy system with a hold full of Diamonds which can be disabled and siphoned legally at leisure) earns a fraction of that.
It absolutely shouldn't pay as high as trade once "it's illegal" is taken into account ... which means it probably needs to pay more than trade before that's taken into account (i.e. it would pay better if you always got away with it, which you won't). If crime pays less than similar honest work *before* the consequences for breaking the law are taken into account, then people don't tend to bother in the first place. (Or alternatively, people should be deterred from becoming pirates by it being illegal, not by it being unprofitable)
Piracy-based missions about recovering a very small quantity of unique cargo for a multi-million payout per tonne, that might be worth it, I guess. Can't see how anything less extreme would work.