Sister post to this. (I think they're basically the same idea but I found myself typing "and" when making the title of the last one so here we are)
I would like to be able to combine hosted layers into one group layer (see below) after they are published without having to export to a local GDB and overwriting the old layer(s), since that is 1) time consuming and 2) error prone. It also still makes the user have to manually get rid of all the old layers. What I want is functionality more similar to adding new feature classes to a feature dataset. (If we could do this in Pro that'd be amazing, but I think that's too much to ask).
For example, each of these services was created with only one feature class in them (because I didn't know what I was doing at the time and didn't realize that they could be together). All of them could be combined into one service/layer to 1) Make it easier to manage and 2) reduce the clutter on the screen since we still don't have nested folders.