I don’t see the problem with “leeching” – you sacrifice the visits of 4 alts and can’t do anything else (like disruption or winning medals) with them for the benefit of the 5th alt. Of course only one alt in a raid should get vanilla. If you have a few alts leeching in a raid all members will get less vanilla.

Basically raids are then a boost for your main, some vanilla scoops additional to those you get by soloing. Raids shouldn’t be too powerful but they can easily be balanced just by changing the number of participants. All those artificial restrictions like only one raid every 60 hours wouldn’t be necessary.