I haven't "taken" any assets. That's not how Workshop even works for Cities:Skylines, per se. None of my park area buildings rip anything off. I've simply created park area buildings for many props and buildings that couldn't be otherwise added as an actual part of a park area in Parklife. You must still subscribe to those props and buildings as posted by their originators. Also, very few of the models in this project are original to Cities: Skylines, themselves being derived with and without permission from other sources. In my case, I've asked for permission in many cases, even though it wasn't actually necessary due to how Workshop allows sharing of props without actually copying them.

Is every asset you make taken from someone else?