Kahl and now Duviri are alternate game modes with very little to do with the core content, yet both of these hard block important core game progression systems, the Archon Shards and Incarnon Genesis adapters. These are Warframe rewards that are only useful when full Arsenals are available, therefore these should be earnable from Warframe game modes where they are actually relevant. There's no need to remove Kahl or Duviri as an alternate source for these things, but as an exclusive source it kills interest in keeping up with the progression of this game for core Warframe lovers who have no desire to spend their valuable time on "some other game" just to progress in Warframe. Now to preempt some posts:
"Haha you don't get the rewards! Loser!"
"You can just quit Warframe if you don't like it!"
"But there's other stuff to do, like replaying base star chart E-Prime."
"Suck it up, games aren't supposed to be fun, you gotta EARN your rewards like a job!"
"My time isn't valuable, therefore neither is yours."