One quick change would be something like this:
update loottable_entries set probability = '100';
That would make all loot tables always drop at least 1 item. How often the individual items drop would be determined by how many items are in the group, which has no quick fix.
Though, if you are getting good drops on Grand Creation then you should on the PEQ db as well, they are one in the same. I think this may just be a luck factor in your case
A group can run through a zone on Grand Creation talking about all the great drops they got, and another group can run through complaining they got nothing.