Evil is something like a foreign virus which managed to invade the body of Creation. It exists, but people must reject it by abstaining from actions associated with evil or leading to it. Sinning makes evil grow.

It's not the manichean principle in which good and evil are complementary notions.

In SW, the Zoroastrian inspiration is transformed in a dark side of the Force that musn't be used, or evil will grow and destroy the cosmic harmony.

In WOT it's very similar: the shadow might have a cosmic role, but that role has it outside of Creation, barely able to touch what's inside (the role of that small brushing of the Lord of the Grave on Creation seems fairly obvious: it's to allow everything in Creation to decay and to trigger the transition between life state and death state, without making death final.). The Bore allowed Shai'tan to touch what's inside Creation in a larger way, and the more people have embraced its service the more it spread like a virus that would eventually destroy Creation.

As for Taoism, your understanding of the Yin Yang and what it represents is completely wrong (and seems to derive from wrong notions about WOT, where you associate the Shadow to the dark part and the Light to the white part, when this is strictly a representation of the harmony between the female and male aspects of the Light).

The Yin Yang is not good vs. evil. It represents the whole (thus the circle) in harmony, the female (dark) and male (white) aspects in balance. Female/Male isn't just the gender, but a whole set of opposite values/aspects that is associated with each (solar and lunar, wet and dry, active and passive and so on). The dots represents in turn the small part of female aspects in a male and vice versa, and the fact no aspect should dominate at the complete exclusion of its opposite. The symbol doesn't have to rotate (and has nothing to do whatsover with the Wheel of Time/Wheel of Suffering), that harmony doesn't purely mean constant equality between the two aspects, that one sometimes have to dominate, is already represented by the shape of the halves, each with a thin end and a large end, and the dots are placed in the large end.

The taoist aspect in Star Wars has nowhere the importance it has in WOT, and is pretty much limited to the dynamics of Anakin/Padmé and Luke/Leia. In WOT the Taoist inspiration is much greater as the equivalent of The Force is split in male/female aspects, and gender balance is a main theme of the series. But like in SW, the vision of good vs. evil isn't Taoist but mostly Zoroastrian.

In Taoism there's no Evil, evil is strictly an ethical concept, associated with behaviours disrupting cosmic harmony. It isn't represented in the Yin Yang, no more than evil is represented in WOT in the symbol of the Aes Sedai (the whole one, not the third age halves).