They need to get rid of the split like this and just do something like Trickster's most efficient system (no share, but the exp bonus increases for each member). Like, have the party bonus start at +10% and go up to maybe +30% in a party of 6. Stops leechers and promotes actual party training.
Only problem I can see is that you can still "leech" the exp boost (even if it's somewhat minimal) off of other members (like Archmages getting a free exp boost from having an HB mule). So yeah, it's not a perfect system, but it's not nearly as bad as the current system (especially if they don't go to TO's extreme and do 2.5x exp in a full, specialized party).
Only problem I can see is that you can still "leech" the exp boost (even if it's somewhat minimal) off of other members (like Archmages getting a free exp boost from having an HB mule). So yeah, it's not a perfect system, but it's not nearly as bad as the current system (especially if they don't go to TO's extreme and do 2.5x exp in a full, specialized party).