The question came up not too long ago if we used the Lightmixer, and we had to answer that we did not. There were various reasons for this, but I meant to follow up with some suggestions to make it easier to adopt in many shot production scenarios. Honestly the main limitations for us are that it doesn't really support the creation of light rigs, and makes editing lights a bit cumbersome.

• We can create light primitives through the teeny-tiny icon menu in the top right, but we wish the whole 'creation' aspect of the mixer had a stronger role. It currently seems like almost an afterthought for a node designed mainly to edit existing light prims.
  
• Rename lights: I can't find a way to rename light prims without using the parm editor or diving into the auto-generated subnet and changing it there
  
• Add intermediate transform prims: creating light prims is vital, but we also need to create light rigs, where we group lights together under transform prims, perhaps even nested transforms at times.
  
• A Drag and Drop mechanism would be great, similar to what we have in the Stage Manager, so we can configure our lighting hierarchies without having to edit prim path parameters.
  
• Editing light attributes... The pop-up parm window is bit awkward to use... every new light you create spawns a new pop-up. If you close one of them, you can't recall it. A nested parameters pane within the lightmixer UI would be handy to let us select a light from the list and edit it. Currently if we have the Mixer selected, it takes over whatever parameters pane we have open. And just TBH... artists aren't going to be bothered with the pin-fu necessary to pin things just right. The attributes tab in the Mixer is handy, but customizing that requires some external config changes. Would be nice to just select a light from the Mixer UI and have its full parms readily available right there without futzing around.
  
• when we create collections from the little folder icon in the "Lights" panel, we get new collections, but where can we edit their contents? How can we add or remove lights from those collections? When right-clicking on a light in the list on the left, the 'Add to Collection' command is consistently disabled.
  
• Attributes vs Transforms... these display data very differently and it can be a bit jarring. The transforms tab can potentially show the full USD stage, or part of it. The Attributes tab only shows a very minor set of attributes, driven via config, but without any hierarchy. Visually it's just a bit confusing. I can't help think there is a more user-friendly way of letting the artist make edits to these. But a nested parm window would be a good start at any rate. A spreadsheet approach is cool for sure, but it's jarring having to use two tabs to edit the same light, depending on what you need to do.
  
• collections appear in the Attributes tab, but we can't tell what prim they exist on, and we can't seem to edit them.
  
• the list of lights on the left will frequently not update when a new light is created.
  

Anyway, in its current state, the Lightmixer doesn't let us generate and structure light rigs, so we are doing things manually. It also makes editing lights difficult due in part to bugs, and in part to missing functionality. But I'm convinced of the need for some sort of node like this, to help us manage the creation of complex light rigs, as well as edit light prims in an incoming stage. (I also appreciate that Houdini has other procedural tools like the Duplicate LOP and ForEach blocks that can be used in the creation of light rigs, so a one-stop-shop node like this is far from self-evident.)

I agree to all your points, we have the same situation, we wanna use the light mixer but always end up organizing everything with light nodes because it simply is less cumbersome.