I feel like if you have a controller that is branded for both, the latest released console should take priority if you had to pick one. I can't imagine they would market a controller towards the 2600 and say "but wait! You can also play this on your Genesis"
Even if they did, it just makes more sense to pick the later console.
Besides, the Fighting Commander Controller is only marketed to the SNES classic, not the Wii U or Wii at all. The NES classic extension cables have a very small blurb that they can be used with Wii or Wii U Pro Controllers, but that's it. It says "For NES Classic" right on the front of the box.
IMO it
only makes sense to make a dedicated console "accessory" section under the dedicated console subheading for this, the NES classic controllers and extension cables, etc.