TF exists for people who don't raid or do something else besides raiding, it's nice to see some random piece of gear to TF. However, I do think that TF should be capped at mythic gear ilvl.
As for difficulty removal, honestly, I'd remove either N or HC, there's too little difference between the two, ofc they add some mechanics in HC, but difficulty-wise it doesn't really feel like a proper step up.