Don't know if this is intended but I've noticed that at least with Hazel the answer to almost all troubles against bosses is to just spam GC in a very reckless fashion back and forth due to the iframes it seems to provide and this will actually be enough in terms of dps to even get S+ on all of them so no need to even bother stacking Karma which is kind of a bummer.
I also have to ask, is it possible to get Burst on the stages that unlock after beating the game or is vanilla S+ is the most you'll get due to their nature?