The primary issue with the
The primary issue with the Ioniq is its use of real leather (more emissive) and a dual clutch transmission instead of a planetary gearset eCVT. Clearly, since the DCT has far more components and is made to the lesser Hyundai standard when compared with the Toyota standard, it is going to be far less reliable. I'd say the same probably applies to the engine as being less reliable.
Also, having driven one, it is very significantly less smooth than the Prius is.
I'd be willing to bet that the Ioniq also hypermiles worse since it has a higher minimum engine rpm due to the transmission type.