The rate they drop actually depends on your current forms level, the higher your level is the more of them will drop and the higher grade ones as well to make leveling lower leveled form easier. And I agreee, I also had hundres of them besides avoiding most fights for testing purposes in my runs. There currently is no diffrence in difficulty but that my be an interessting idea for later implementation!
Yup to keep balacing more manage able they get removed as well as exp shards and are returned after the forms story is completet. That also is an good idea! I will add an extra text in the Party Member Tutorial and warnings! Thansk^^