So I'm a person who absolutely loves rhythm games. And I think that while the gameplay mechanics of a rhythm game and a quick-time event could be boiled down to the same thing (they're both centered on timing actions) I think rhythm games are much more involved and challenging than quick-time events. Quick-time events give very few prompts and a generous amount of time to complete the action in time and usually last for a few seconds before regular gameplay resumes. Rhythm games on the other hand involve hundreds of prompts one after the other in quick succession, for the duration of whatever song they're synchronized with(so about 3-4 minutes usually) and involve more complex patterns than quick-time events. So while both share the same basic elements, I vastly prefer rhythm games due to it requiring more concentration, stamina and dexterity, not to mention they come with some pretty awesome music.
But yeah, I agree with the statement that rhythm games are like quick-time events' big brother. That's a pretty fair point.