This meme has become rather tiresome, so let me just explain why you're wrong.
First, the mini-hakkero is more or less simply a tool that produces immense heat. Is that an advantage that gives Marisa a leg up over others? Sure. But the applications of said power, such as the Master Spark and its variations, are products of her own ingenuity and experimentation with the tool. Without a proper handler, the mini-hakkero is nothing more than a paperweight that can heat your home (which is pretty much all Rinnosuke was doing with it before he gifted it to Marisa).
Second, it seems like few of Marisa's attacks actually utilize the thing. There's no mention of it pre-PC98, so it's safe to say that things like her flight, basic danmaku, and variations on orreries sun, are all products of her own power, and not the result of the mini-hakkero. As well, DDC shows us that she can still utilize illusion laser and magic missiles without her hand furnace, as well as utilize fairly powerful and complex spells such as Magic Absorber. Really, the only thing we can even prove that she uses the mini-hakkero for is the Master Spark, which makes sense as it's a massively powerful spell, especially for a human. But, to say that Marisa is defined entirely by that one spell is not doing her enough credit, and it's worth noting that her only confirmed route (Marisa B, UFO) didn't even have Master Spark in its repertoire, meaning that she likely didn't even need it to resolve that incident.