RSS and Atom are great. And I wish I could get every newsletter as feed instead. Emails get lost in the daily avalanche, but RSS/Atom feeds know to wait until I have time to read. But they're already beset by problems with lack of adoption. Any alternative syndication tool is going to make it even harder to reach your audience.
I'd also be careful about platforms like Medium. I wanted to like Medium, I really did, but the algorithmic feed's constant stream of clickbait quickly grew tiring. I ended up muting it, newsletters and all. It seems to me that any platform that has an algorithm is setting up a hostile environment for people who don't enjoy producing or consuming clickbait.
I believe you can also however add on to Atom/RSS. Many feed readers now also support the WebSub [1] standard which allows them to receive instant push notifications of new articles. It kinda speeds up getting things as you don't have to rely on exclusively the pulling model. Sites like WordPress, Blogger, FeedBurner, Mastodon, and Friendica I believe are all examples of sites that support it.
It basically extends Atom/RSS to have another feature. Clients that don't support it can still pull like normal. Wikipedia summarizes the technology a bit nicer than the first link [2]
