Intervals are ambiguous on the staff in the traditional system. They're disambiguated by reference to the clef and key signature. The whole point of this new system is to remove that ambiguity so you don't constantly have to keep the clef and key signature in mind when analyzing intervals.
Fair point. I can see how that might be nice. I will say that, if you play music a lot from traditional notation, that ambiguity completely disappears into the background.
