I've published 30+ books for young readers.
22 - were my own (based on my own characters, concept, etc, some in collaboration with co-writer husband and/or illustrators)
9 - were IP (based on pre-existing characters/concept from DC/Marvel, etc.)
The writing process is the SAME.

There's no true generalities about IP vs. your own copyright. Some of the content owners were more hands on, some were totally hands off. Some of the books ended up being bestsellers, some went totally under the radar.

No matter if the original character and story idea was mine or someone else's, the process of writing the story remains the true challenge. (Writers often lament: ideas are cheap, execution is everything.) I poured as much care, craft, time, and love into my IP books as the rest.

Something that is DEFINITELY true: IP books are less likely to win awards (unless kid-chosen) or receive starred reviews or garner other critical marks of success. *shrug* I get it, there's a bias, but I can tell you for me, there's zero difference in the art of it.

Oh! And another thing: I doubt anyone from the outside could predict which of my IP books were monetarily lucrative and which weren't. Every deal is SO different.

Something I've learned from IP: DO NOT do it for hope of future windfall. Do it because:
1. you love the characters/world so much that just getting to write it is worth it to you
2. and the advance itself is enough money to make it worth your time