If you are focused on how Scrivener looks, then you might be missing the point of Scrivener. The idea there is to be immersed in your book and the writing of your book, not the app itself. Scrivener expects you to be thinking about your characters, research, story, dialogue. The full-screen writing mode is a typewriter. Ideally, when you are using it, you would be in a comfortable chair, maybe some music playing, and just hack away at your writing project. Scrivener expects you to go into full screen mode and write 5000 words, then come back out to use the other tools to prepare for another full-screen session of writing 5000 words.
Similarly, if you are focused on how the text looks in a Markdown editor, then you might be missing the point of Markdown. The idea there is to focus on the semantics of what you are writing, completely separate from the way the text looks. In the final product, the italics might be shown in dozens of ways, with extra letter-spacing or slightly larger font size, but you don’t think of that when you are writing because what matters when you are writing is the semantics of italics. The emphasis that you are putting on a word or words. You want to be thinking italic emphasis, not thinking “this should look italic.”
I’m sympathetic to your point because I also do visual art and the way things look matters to me. But when writing, we have to put that kind of stuff aside because writing is something that takes 100% of our focus and effort to do well. If you are a fan of George R. R. Martin’s “Game of Thrones,” consider that he literally writes on a 1983 MS-DOS PC. That is one of the ugliest things every created. The radiation alone is problematic. But the reason it may work for him is because there is nothing there to distract him from his story and characters. Which obviously, have captivated millions of people.