- Edited
You know, now that you mentioned KDP, you made me curious enough to check their stated conditions to put books online to sell and I have surprisingly found out that most of the things some people consider the two greatest drawbacks from webnovel contracts are almost exactly the same.
like this two paragraphs in KDP license:
You will retain all intellectual property rights you may have in submitted materials. Subject to those rights, Amazon.com will be the exclusive owner of any permitted modifications that it may create.
You agree to indemnify, defend, and hold harmless Amazon.com and its affiliated companies from all claims, judgments, damages, and expenses (including reasonable attorneys' fees) that may arise out of any alleged breach of this warranty.
As you see in paragraph one even if you are retaining the original rights, you are actually giving Amazon permission to create derivative works from your novels and in paragraph two you are hold liable to all possible claims that may damage their reputation.
source : [link]https://www.amazon.com/gp/help/customer/display.html/ref=hp_left_v4_sib?ie=UTF8&nodeId=201995010
So the only benefit I can see from using KDP is to have a bigger share of the revenue. But then again at least Webnovel do a very good work of promoting the novels of a contracted authors, so probably they gain more money, at least at the beggining.