There are still differences between what most boxing does and the UFC. Most boxing shows are organized so that the promoter handles the talent and the event, and then they receive revenue by licensing out the broadcast rights of that event. That's why the presentation for an event on Shotime will look different than if it's on HBO, even if it's the same promoter. The UFC handles it's own production. Which means what most boxing organizations have a pure revenue actually has an expense for a UFC event. Now, obviously, the UFC gets compensated for the broadcast rights, but if that compensation exceeds what a boxing promoter gets after the costs of the production isn't known, as far as I've seen. However, the blanket % of revenue numbers are not directly comparable, because there are costs associated with each organization that are different.
This is true when comparing Bellator's revenue split with the UFC as well. Bellator is selling it's broadcast rights to it's parent company, for an amount that I'm sure is the most beneficial to that parent company from an accounting standpoint. Which means it's revenue is whatever Paramount wants to pay Bellator, plus ticket sales. They could theoretically have a system worked out where Paramount pays a flat percentage above talent compensation and brag about how big a piece of the pie fighters are getting. But that doesn't mean Bellator's worth is only the number that Paramount is willing to account.
This isn't to say that I don't want fighters to make more money. I do. But these arguments about revenue split are not the end all be all of the conversation. There are plenty of things that the UFC does that aren't factors in other sports or even other leagues. The enhanced USADA drug testing is one example. Bellator just lets the commission handle that. Health insurance is another. And the aforementioned production costs. It's a false equivalency to look at just a percentage of revenue and assume one side isn't paying enough. DWTNCS was paying guys 5k to show, 5k to win in 2017, and I think it's higher now. Bellator had guys fighting 2 weeks ago for 3k/3k. It isn't going to change until there is another place people can go to make money, and it wouldn't matter to a guy at that level what the revenue split is if he's going to get nearly the same show money from one organization as he would show+win from another.