Check this diagram and tell me it's simpler than an engine and transmission.

https://automotorpad.com/toyota/83449-funcionamiento-sistema...

It's essentially an engine, a transmission, another transmission (power split device), a drive motor and a generator.

Most of the images there are broken, all I see are some conceptual block diagram type things. Find a teardown of the hybrid unit and compare to a teardown of any automatic, look at the actual internal complexity and moving parts. I was surprised. Here's a video of the P710: https://m.youtube.com/watch?v=O61WihMRdjM