Building Prowess from Grounds of Valor is by far one of the most frustrating new pastimes in this update. There are 11 Prowess effects that are randomly chosen from, as as far as we know, 9 levels of prowess. If you're doing pages in order to get more treasure casket prowess, you're stuck in the same area potentially for days, unable to leave so you won't lose having a chance at higher brown box drops (without, the drop rate for chests in GoV zones is rediculously low).
As far I can tell, there's no reason why keeping prowesses would be overpowered - keeping the buffs would not only be less frustrating for casket hunting, but would also enourage soloers to have more options for zones, picking whichever they have the most prowess in (for example - crafters looking to farm crystals will return to the zone they have the most crystal prowess)
Another solution could be that instead of making the prowesses randomly generated when the last mob is defeated, make the prowess you want to get/upgrade selectable when you return to the book. Some prowess buffs are completely wasted on jobs and having them randomly picked from 11 is annoying. Being able to pick if you want magic attack or cure potency would be considerably better than doing a page to get a prowess thats wasted on your job. This would make farming much better as well as making partying more fun - but the way things are now it would be like every time you went into Abyssea if you got random atma assigned to you.
I love the concept of GoV and hunting for new chest items, but spending 3 hours in Zerhun mines as a BLM with my highest prowesses as Weaponskill damage and attack/accuracy is annoying to no end. I thought it'd be an easy way to get skillups as well but grinding for several hours so you can have a better rate of it seems like no improvement at all.