It would be nice if parented actors could also remember if the outliner view was expanded or not when reopening the level. Currently folders stay closed if they were closed when the level was last saved, but the parented actors do not, even though the hierarchy is visually indicated very similarly.
Editing multiple objects is a pain, you cannot select a component to change its properties from the component list when multiple actors are selected, even if all the actors are the same when it comes to their components. It can be tricky to determine I guess though since you can add and remove components from instances. One can always make instance editable parameters in the actor class to control component properties.
Grouping is just… meh. The group actor clutters the outliner. It’s moved out of the way by default (but this also moves it away from the grouped actors). Grouping feels like a way to manage some visual-only small clutter, for that the selection box can be nice, otherwise, I’d use the other means.
Personally I just try to pack bigger level elements that logically go together into big dumb prefab-esque blueprints, also resorted to using scripts to spawning actors where patterns are found (EditorPostEditChangeProperty is nice with that) which also neatly allows me to parent the generated actors to whatever created them. Which is where it would be nice if all child object hierarchies wouldn’t be exploded when opening a level.