Any challenge in this Tactical event that’s using a specific weapon completely relies on luck rolling into a game using that weapon, which you could conceivably not do for hours. Even ending an opponent’s spree is essentially out of your control because it relies on opponents doing well.
It’s just not fun. And you can’t even quit out to find the game you need.
Challenges in general…if they’re the sole way of progressing…ruin the game.
The concept of challenges is fine, but the implementation so far… 
XP from challenges should be as a bonus, while XP for actually playing each mode correctly should be the main goal.
The fact that you get the same base XP whether you or win or lose a match is insane.
They need to make challenges fair & less frustrating for to do while not changing the way you play, I don’t mind doing challenges, but I don’t like dumbing down how I play to complete a grindy challenge