A Mix Node with more socket Inputs is something that should be there by default in the Node Editor as another option .I think for a more user friendly UI, tools like this are needed to avoid the user becoming distracted by the complexities of the software and let them focus on their goals.Yes, you can create a Node Group of several mix nodes but it is a task that makes you go out of your way in this case to achieve something that should have been there in the first place.
Everything that can be done to make the users workflow more simple & faster is beneficial and I think beneficial to all users levels, Advanced, Intermediate and new comers, and a very good job is currently underway to improve the UI in Blender with that goal.
A Multi-Channel Mixer Node could be compared for example to a mixer with many channels in a recording studio to which you can plug mics to each of its channels audio jacks and so on.