From a utilitarian, “f/8 and be there” perspective, my iPhone today is way way better. I always have it with me and it handles pretty much any light condition I encounter, including near darkness.
And I took a 4/3 mirrorless digital body with a zoom lens to Africa recently, and got tons of sharp, well-exposed photos of wildlife.
But a slide is a picture, in a literal physical way. There’s no format or device needed. I hand it to anyone, and they can hold it up to a light and see the picture. It is a piece of art the way a sculpture is a piece of art; it embodies itself. I can keep it like a book, hand it over, pass it on. That is very cool, and looking through my old slides is satisfying to me in a way that opening up my laptop and scrolling through pixels is not.