I have no basis for this, but here's a theory.
Danmaku is like combat sports. Combat sports are pretty much martial arts in game form. It's got rules, and is generally less dangerous.
There are two types of danmaku.
Danmaku as a part of the danmaku system is what we generally see in the shooters. It's bullet/laser based, must be dodgeable, and is not lethal. There are rules.
Danmaku as a part of magic and magical battle, however, is a different story. Not bound by the rules of the danmaku system, attacks are more varied (can be physical attacks, more usage of innate/youkai abilities, not in bullet form) and much more potent. This is a real fight.
Makes me suspect that danmaku spellcards are actually modified versions of *real* spellcards, specially made to be more mesmeric but also dodgeable. Real spells are like protagonist bombs/spellcards, and stuff you might see in the fighers that obviously don't look like danmaku (Mishaguji) or should be inescapable (Royal Flare).
Maybe. This theory obviously has its own inconsistencies, but I'm just putting this out here as a thought.