I don’t know if treasure charts need a buff this extreme. When I do rare+ treasure charts I always get back-to-back golden chests (I have an exotic enchant). The loot is fairly okay, I usually just get arcspheres, but nothing exciting or fun. I think a buff that guaranteed rare items would be fine, but guaranteeing a rare scroll AND an exotic enchant might be a bit much. Maybe I don’t mind the low rewards because I do treasure charts somewhat casually, but you might have a point with the comparison towards dark sea loot.
At the very least a galleon buff would be nice. When I was grinding for the brig I was wondering why doing an exploration-related activity that involves ships hardly gave me any galleons for the next ship upgrade (in fact I was wondering why doing sea activities didn’t give enough galleons for the next ship upgrade). I think there should be “bank chests” which give 300-500 galleons (you get maybe 2-3 from each rare+ chart, more for higher rarities, more if the dude who owns the treasure is a banker or someone with a money-related title), though this is a bit different than guaranteeing items.