Very well said Frog. Although I will say that there are breed tendencies, there are always exceptions. IMO QH are calmer as a breed than say Arabs or TBs. Not because they are "crazy" but because they are more sensitive and inquisitive. (I didn't say smarter)
Now, do these breeds have "tendencies" because of the foundation parents had certain characteristics that have (for the most part) been bred true? I can't honestly say. But is does give one pause for thought.