Easy exploitable idea that will reduce grind .... And since Gree(d) like to keep this game as gringy as possible it will never come to realization.
Just to makes things clear:
ALL heroes use the same 5-6 materials, you can create a farm party with unused champ and farm the items you need ( like FD, +26, DoSP, etc ... ). With the possibility to rise multiple bottlenecks in the same run this would lead to a severe grind drop. That , sadly but true, it's what Gree(d) want to prevent ... Why do you think they didn't even put P.scraps in higher stages?