What we’re talking about when we talk about digital publishing vs mainstream publishing is that loaded word of the internet age: disintermediation.
In the old system, of which many remnants remain, everyone has a hand in the novelist’s pocket. Let us count the ways: agent, subrights agents, publisher, printer, wholesaler, bookseller. Six intermediaries at least. Directly or indirectly, each of these takes a piece of the cover price before that check finally reaches the author.
In the digital system, the fixed costs of editing, proofreading, formatting, and cover design remain. They must be paid upfront, but their providers do not get between the buyer and the author on every sale, as they do in a mainstream publishing deal. If one digitally self-publishes, the only one who's still interposed between novelist and reader/customer is the bookseller. If one uses an indie publisher as distributor, as I'm inclined to do, that distributor also takes a cut, of course, so there may be two entities between author and reader/customer. But that's a far cry from six or so under the old model.
What of the agent?