No PDK in the 919 Hybrid

In looking at the specs, I was quite surprised that the 919 Hybrid does not us PDK. Instead, it uses a 7 speed hydraulically activated sequential gear box. I always thought that you'd need an electronically controlled gear box like PDK to co-ordinate the gasoline engine and electric motors.

[www.porsche.com]

It could have to do with horsepower. I thought I heard/read somewhere that with mega-high horsepower/torque cars, PDK can't be used? I could be wrong, however, since the 918 will use it.