When I think of most of the innovations that came later to text editors, I mainly think of features that make it easier to leverage massive amounts of code written by other people in a collaborative environment. E.g., linters, LSP, autocomplete, version control integration.
Also, perhaps unintuitively, I'd also put window management in that category which is for me the most important text editor feature. I.e., reading and understanding code written by other programmers spread across many files is the most difficult part of my job, therefore window management is the most important feature.
I might even put debugger integration in this category, something I always reach for the debugger for is answering "what is calling this function and with which arguments?"
Just about the only feature I can think of that's not in `ed` and that's not most helpful for collaboration and using libraries is syntax highlighting.