I agree with you re: whole-steps and half-steps. When you teach "what makes a scale major?" in reference to the scales whole and half step pattern, it is then much easier to introduce minor, and scale modes (Ionian, Dorian, Phrygian). Basic theory taught in this way is really not that hard (however, I majored in music in school). If you introduce intervals, then you don't have to say "forget about B diminished. You won't miss it". You can say "B-dimished triad has a darker, more moody sound because it is made up of two-minor thirds. Or a Phrygian mode has an "eastern" sound because its scale starts with a half step.

That said, a lot of work went into the tutorial, and it is certainly well done.