I spotted this post last night when I was browsing the forums and I think the answer to this question is a little more complex then the attention it's being given. The last response was yesterday so I hope people will forgive me if I'm a little late to the party.
Ok first off I'm going to say that simply telling someone that if they can write a story they should get a literary agent and get published is a disservice. Being a professional writer is hard, ridiculously hard. This is a profession where it takes ten years of 'work' before people start to take you seriously and getting traditionally published in the first four or five years is a significant accomplishment.
And there is a reason for that: your novel probably sucks. I mean that 'you' as more of general you rather than targeting whoever is reading this individually, but unless you are truly blessed by the heavens your first novel is going to suck, probably badly.
That said, most web serials are also similarly bad. I took some time and went through all of the web serials I read on this site and several others and thought about each of them, and even the ones I really, really like are bad. At least if you consider them from a traditional publishing mindset. I couldn't even come up with a single case of a web serial that could be published 'as is'.
There's an axiom in writing where your 'first million words' are practice. That you're supposed to write your heart out and edit/revise until you're the best you think they can be and after you're done you throw them out and start over from scratch. That's what it takes to move from the 'novice' stage of being a writer to being an 'apprentice'.
While that seems both cruel and abstract there's a reason that it has stuck around. You learn to be a writer by writing, you have to struggle with it and immerse yourself into it in order to understand it. More than that you need to develop the skills to break down your own work into it's most basic blocks and separate the good from the bad. Kill characters you love just because they harm your overall story and eliminate plot lines and arcs because they don't really bring anything important to your narrative.
Now there are ways to shorten that as well, reading other people's novels both good and bad is key among them, but you also have to learn to break down why they're good and bad. This works with both published works and web serials.
You can also takes classes, attend seminars and read books all around learning how to be a writer. All of these remove roadblocks in your path as you work towards becoming an author. But you still have to write, and you have to write a lot. Before you consider going pro and wasting time and money hiring a literary agent you need to do that.
Now to get back to the original question, I'm not sure what the contract looks like so making an absolute statement is impossible but lets break down one other thing I've seen thrown around, nothing you sign is going to make you a slave or a sweatshop employee. It makes you a contracted professional, which means that for each set amount you write you get paid a certain amount. And that's not just thing with Webnovel or because the company originated in China. You can get a similar deal writing disposable romance novels according to what other professionals have told me.
Could you possibly earn more with a site that collects donations for you, yes. I'm not going to argue that it is possible. But it also makes you a tipped professional rather than a contracted professional. That means that if your readers decide to not pay you, you don't get paid.
Your other revenue option is to have your novel published, either by submitting it to a traditional publisher or by self-publishing. Both of these options are beyond the scope of a single post, but I'll sum it with it takes a lot of work to convert a web serial to a novel, and then you either have to shop it around and face the rejection/revision cycle or you have to self publish and then you have to self-promote because no one else is helping you.
Webnovel is also going to translate your novel to republish over seas according to my understanding, that's a group of readers you wouldn't reach otherwise. Again there is revenue potential there but unless you're hiring an editor and a translator so that you can publish in more than one language, that's revenue you can't capitalize on. Letting someone else do the work for a piece of the pie is pretty standard. When you're small and just starting to write the share they take is bigger, once you've written a few pieces your share gets bigger. Standard business sense.
The last thing I want to touch on is your rights. Your characters, the worlds you've built and everything else. While you will give up part of that, I'm going to be honest with you and say that it's not worth much. I've seen a lot of people get hung up on ownership of their work in these forums and I think there is a gross overestimation in what that's worth.
Unless you have written a truly sweeping epic story no one is going to look at it and want to convert it into a manhua or an anime or a movie as is. There's a lot of editing, revising and rewriting that happen first. Most web serials can't even be published as light novels without major reworking. Flatly the world you built and the characters you designed don't have a lot of value in my estimation, the words you put on a page are what you're selling and that's what you get paid for no matter where you release.
Most of the value in the world you built is only sentimental. It's you being proud of what you did and there's nothing wrong with it. I am aware of literally only one case of where one author built a world and wrote the story and another author wrote a second serial, taking over his world and characters and writing his own vision. And if I remember correctly that was done amicably because the original writer was lost and didn't know how to further develop his own world.
As a writer you also need to be able to let that go and write something else. You're a writer and because of that you have more than one story in you. Even if you sell one and you find yourself getting the short end of the stick write another and get a better deal. You might write four or five before you get the terms you want, but that not unheard of either. If you're writing to break into this professionally it's what you'll have to do, and if you're writing as a hobby and hoping to earn a small secondary income then you're probably not super paranoid about your contract anyway.