Nah, that award would go to the Tangut Script (西夏文), used by the Western Xia dynasty in the 11th century: Tangut script – Wikipedia
Here’s an image page from the Wikipedia page. Note that Chinese writing is on the right side, while the Tangut script is one the left side.
I mean, look at the character for 2! It’s only two strokes in Chinese, 二， but in Tangut… holy shit! In fact, other than the character for 8, all of them look insanely complicated.
And below is an example of how you write “mud” in Tangut, from the “water” radical:
You know how to write “water” and “mud” in Chinese? They are 水 and 泥， respectively.
Chinese doesn’t seem so hard now, does it?