Regardless of how we complete quests to get rewards, I think most of the reward balance complaints have either been about hunger or LP. The hunger complaint is something that may be solved by changing the hunger system but lets work with it as is. The LP seems to be about LP rewards that are scaling heavily outside what the game normally provides as it's significantly outpacing curiosities and only getting worse with CHA bonuses rolling in.
For LP rather than pulling a base number from the air, why don't quests dump X hours (plus CHA bonus) into your study window at random. This lets the quests scale with the world because study windows get more powerful as the game goes on. If the CHA bonus hours ever get kind of nutty, this gives a use to really long lived curios (which is another form of autobalancing as long lived curios often have a low LP/hour and high int costs). In general it re-grounds the system in curiosities and helps give some relative sanity checks for current world progress.
Likewise the hunger bonus shouldn't be flat, but scaled by the FEP percentage. Rather than "your stomach has been emptied by 100%" giving you one full bar, it should give you 100% worth of FEP. In the 100% bar, this would be 1:1. In the 300% bar we'd see 1:0.33 . This makes questing viable at all levels of hunger, and significantly dimishes the return for specifically trying to set up a 300% hunger grind questing character. This can still be very powerful or weak entirely depending how the tuning goes but it would certainly spread the potential benefits to a lot more of the game population while curbing the most intense benefits somewhat.
I think the XP bonuses are mostly tuned alright, no one seems to complain about them unless the really tiny ones slip through like <5xp (minimum reward should probably be 50-100xp, mirroring the smallest experience events). I feel like quests that don't merit that much XP reward should just do the dickish "Here's this Q5 dead squirrel" random item handing event instead. At least you know you're getting truly screwed with at that point.
Quality rewards are frustrating because of how scattered they are. Since it's just +1, it's hard to see it as useful when there's 50+ different things it can put that bonus into. Maybe giving the player some agency in the reward by letting them choose 1 of 3 options would help alleviate this. Players could feel like they're having an impact on potentially useful nodes, while quest givers would avoid the issue of "Oh that's a grub quest giver, reroll it for something better" which would frustrate a lot of people as a mechanic imo.