What role does Taliyah fill?

She plays like a control mage in mid, trying to zone her enemies, but she has no tools to control that zone at all.

Her passive and the worked ground make you feel like she should be a mobile skirmisher, but she doesn't have any actual mobility in a fight.

Her short range abilities make you feel like she would blow up things that get in her range, but she has no damage or bulk to be found.

Her ult makes you feel like you should be a ganker, but she lacks any significant waveclearing ability, so she can't easily leave lane.

Her W+E should at least be able to help peel with the slow and knockback, but this is so specific and unreliable that it wouldn't actually work on anyone.

What is Taliyah supposed to do? She excels at nothing, has no clear role, and not enough in her kit to fulfill any purpose. It is a reasonable question. This may be why her winrate is so incredibly abysmal, and no one plays her at all.

Honestly, the complete failure releases like Taliyah and Illaoi are very frustrating, especially since Riot tries to forget like they ever existed by never even adjusting them afterwards or addressing the major design flaws with them.