I think DTube's 25% cut is justifiable. They do have development and maintenance costs associated with their platform, and like you said, they often share the proceeds with their participants. I earned close to $20 for a DTube upvote, so they definitely gave me more than they ever took.
But this post should be a warning to those who make use of alternate apps to be aware that a cut of their revenues may be taken. But so far I don't see any abuse in this realm.
That is hard to argue against because @dtube probably has the most expenses out of all of these platforms. Plus, they've proven that they're using this money to fund advancements. It takes a lot of money to pull off what they've created for us. I wish each of the platforms listed here who are taking rewards would have a monthly expense sheet that we could all view so we know where our rewards are going. That would put a lot of people's mind at ease.
In the case of DTube, they're going to need tens of millions of dollars to make it work as it scales. Storage costs are enormous, easily in the millions, this is why our videos keep getting deleted, they cannot afford to store them all. Developers are mighty expensive too it seems. A small team of full time developers costs millions as well. The enormous operating costs of running a video sharing platform is the whole reason platforms like Vidme failed.