As this is doing numbers let me elaborate a bit.
The traditional definition of what counts as original is indeed quite restrictive. Obviously once civilization advanced and writing spread, all writing was likely to be influenced by some other. Still we must acknowledge the influences.
Some derived scripts were more innovative than others. Latin from Greek was a very small change. Greek from Phoenician was a pretty big one. New category, abjad to alphabet.
Brahmi from Aramaic was also a big jump, abjad to abugida. Indians deny the descent but they deny everything.
Hangul was very innovative too, but the influence of phagspa is undeniable.
At any rate, if you change the taxonomy to classify the more innovative scripts as original, you get a category including hieroglyphs, Chinese, Brahmi, Hangul. If you include those with no graphic resemblance, you get those plus Glagolitic, Georgian, Armenian (made to look different to Greek on purpose), Deseret. Those just aren't useful categories at all.
The traditional taxonomy on writing system is about understanding the history of the spread of writing. And the history says there are two extant branches, Egyptian and Chinese. QED.
Every single living writing system besides Chinese is descended from Egyptian through Phoenician.