> the minor scale doesn't count because C major = A minor if you start on A, fair enough, forget that one.
It might actually count since the harmonic minor exists. But this is just stressing the point that all of those "separate" scales might perhaps be best introduced as simple variations of the usual diatonic scale. Then sure, you might want to practice them a little bit, but at least you should have "learned" them in that you are not wondering what you're supposed to play.
Even though they don't all have seven notes? (Why is a seven-note scale called "diatonic" anyway, that should mean a scale of two notes, doesn't sound very exciting.)
> Why is a seven-note scale called "diatonic" anyway
The prefix of "diatonic" is "dia" ("through"), not "di" ("two"), but nobody really knows what exactly its origin (διάτονος, "diátonos") was supposed to mean[1]: it's probably either something like "through the tones" or "stretched out tones".
The second meaning is closer to the modern definition we have for diatonic: the 7 (out of 12) notes are selected to be as stretched out as possible in the octave, that is, each adjacent note is either 1 or 2 semitones apart, and the two 1-semitone-apart pairs are as far as possible from each other (note that the second requirement excludes e.g. the ascending melodic minor[2] from being considered diatonic, even though it has 7 notes).
Which seven notes matters. At least on a guitar you only get 7 or 12. Some pipe organs have 15 notes which allows them to sound much better when you choose the right one (but some keys are horrible despite having 15 notes to choose from where as the standard 12 is an acceptable compromise for anything even if it worse where the 15 work). Violin gives you infinite choices, and I've seen keyboards that have 50+ (look up microtonal music). You can also remove the frets from a guitar - I've heard of one person (exactly one person) doing that.
It might actually count since the harmonic minor exists. But this is just stressing the point that all of those "separate" scales might perhaps be best introduced as simple variations of the usual diatonic scale. Then sure, you might want to practice them a little bit, but at least you should have "learned" them in that you are not wondering what you're supposed to play.