User blog comment:B214/Volume 22 spoilers/@comment-73.46.6.122-20161126201153/@comment-30289101-20161126234317

If I had to guess, it's because of how dangerous it is for Valerie to use the grail at that level, So it's probably a self imposed limit to how much of its power she uses. And while Asia's power can't do things like remove weakness and probably can't revive the dead, her healing isn't inferior to the grail; her balance breaker is basically a version of limited industructability while it's active.