It turns out that cherry picking spells out of the curriculum is hard. There’s a method to Hogwart’s madness in teaching so many seemingly useless spells (seriously, who is ever going to want to turn a mouse into a snuff box?) and it has absolutely nothing to do with magical power, as far as I can tell. Instead it seems to do with the shape and form of the magic. First Year spells require effectively zero adjustment. You say the words and make the wand movement and push an appropriate amount of magic into the wand and you get the spell, every time. I can produce bluebell flames for days, now. Spells from higher years seem to require you to feel your way through the spell and adjust it more than what the wand movement is capable of, with the wand movements of NEWT level spells providing a very rough shape. Each of those useless spells thus teaches you to recognize and feel out common adjustments required for various kinds of spells, as I’ve noticed that spells that share wand movements and have approximately the same complexity have identical arithmantic functions in the more advanced books I have access to.