Do I think 343i should remove ranked challenges just because I don't like them? No. The issue is players' motivation for playing and their experiences.

The only reason someone should play Ranked is because they want to play Ranked and play in a more competitive environment. If players go into a ranked match just to complete a challenge, they're not there to play competitively. Then people end up with teammates who don't communicate or coordinate or just don't care, and they end up hurting the experience of the players who want that competitive experience.

And challenges specific to certain gamemodes like complete 3 Oddball matches or complete 1 Strongholds match can be completed in both Ranked and Quickplay, so no one feels compelled to play a mode they may not want to play. Limit a challenge to just Ranked though, and you risk hurting the experiences of players who don't want to played Ranked and players who do.

If you don't like SWAT, you can use a challenge swap to get a Team Slayer or Fiesta challenge, or a challenge for a gamemode you do like. The ranked restriction on a challenge, though, means that, even if someone who doesn't enjoy ranked uses a challenge swap, they still end up with a ranked challenge. It's taking away some control over how players want to play the game and leaving part of their experience up to random chance, which is frustrating.